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  STATE OF CONNECTICUT v. LUIS RODRIGUEZ
                (SC 18945)
        Rogers, C. J., and Norcott, Palmer, Zarella, Eveleigh,
                    McDonald and Espinosa, Js.*
      Argued May 14, 2013—officially released January 28, 2014

  Elizabeth M. Inkster, assigned counsel, and Kelly
M. Berwick, deputy assistant public defender, for the
appellant (defendant).
   Leon F. Dalbec, Jr., senior assistant state’s attorney,
with whom, on the brief, were Gail P. Hardy, state’s
attorney, and Vicki Melchiorre, senior assistant state’s
attorney, for the appellee (state).
                          Opinion

   PALMER, J. Following an incident in which the defen-
dant, Luis Rodriguez, stabbed and seriously wounded
the victim, Angel Salvador Diaz, a jury found the defen-
dant guilty of assault in the first degree in violation
of General Statutes § 53a-59 (a) (1).1 The trial court
rendered judgment in accordance with the jury verdict,2
and the defendant appealed to the Appellate Court,
claiming that the trial court improperly had permitted
Diaz’ attorney to testify about an immunity agreement
that he had negotiated with the state on behalf of Diaz.
See State v. Rodriguez, 133 Conn. App. 721, 728–32,
36 A.3d 724 (2012). The Appellate Court rejected the
defendant’s claim and affirmed the judgment of the trial
court; id., 732; and we granted the defendant’s petition
for certification to appeal, limited to the following issue:
‘‘Did the Appellate Court properly conclude that the trial
court acted within its discretion in permitting testimony
from the attorney for [Diaz]?’’ State v. Rodriguez, 304
Conn. 915, 40 A.3d 784 (2012). We need not resolve this
issue, however, because, even if we assume, without
deciding, that the trial court improperly permitted Diaz’
attorney to testify, the admission of his testimony was
harmless. Accordingly, we affirm the judgment of the
Appellate Court.
   The opinion of the Appellate Court sets forth the
following facts that the jury reasonably could have
found. ‘‘On February 7, 2008, Diaz was working at the
Brook Street Market [market] in [the city of] Hartford
. . . with two other employees, William Ramirez and
Franklin Ramirez. . . . Diaz, William Ramirez and
Franklin Ramirez [knew the defendant] because he
lived in the neighborhood and frequented the market
where the three men worked. On the afternoon of Feb-
ruary 7, 2008, the defendant entered the market and
asked Diaz if he could borrow [$20] from him. Diaz gave
the defendant a [$20] bill. The defendant exchanged the
[$20] bill for twenty [$1] bills. Then, as patrons entered
the market, the defendant handed them one or two of
the [$1] bills. After giving away all of the bills, the
defendant left the market. He returned a short time
later and asked Diaz if he could borrow [another $20].
Diaz refused. The defendant told Diaz, ‘fine, we’re not
friends anymore. . . . I’m Espana; you’re going to see
what’s going to happen,’ and left the market.
  ‘‘At approximately [10:15 p.m. that same day], Diaz
and William Ramirez took garbage out to a dumpster
located in an alley behind the market. As Diaz was
depositing garbage into the dumpster, the defendant
[who apparently had been lying in wait for Diaz] stabbed
Diaz twice in his left side with a knife. After stabbing
Diaz, the defendant ran away with the knife in his hand.
Diaz returned to the market and, while bleeding pro-
fusely, told Franklin Ramirez that the defendant had
stabbed him.’’ State v. Rodriguez, supra, 133 Conn.
App. 723.
   ‘‘[I]mmediately following the attack on Diaz, police
responded to the market. . . . Diaz told [one of the
responding officers] . . . that ‘he was approached by
two black males . . . [that] they demanded his wallet
. . . [that Diaz] declined and [that] one of the black
males stabbed him.’ When asked by the officer whether
he could identify his attackers, Diaz stated that he could
not. During this brief exchange, Diaz was ‘distraught’
and ‘had a blank look on his face.’ ’’ Id., 724. Neither
William Ramirez nor Franklin Ramirez informed the
officers what they had observed that evening regarding
the defendant’s involvement in Diaz’ assault. Thereafter,
‘‘Diaz [underwent] emergency surgery and was hospital-
ized for a period of approximately five weeks as a result
of the injuries [that] he sustained during the attack.
  ‘‘On February 16, 2008, nine days after the attack on
Diaz, the defendant returned to the market. William
Ramirez and Franklin Ramirez were working at the
market that day. The defendant, who was intoxicated,
threatened William Ramirez . . . and made a gesture
[by running] his finger across his [own] neck. The defen-
dant stated to the two men that he had stabbed Diaz.
Police were called to the market and arrested the defen-
dant, who was belligerent, resisted arrest and threat-
ened the arresting officer.’’ Id., 723–24.
   ‘‘On March 19, 2008, after he was released from the
hospital, Diaz [who had heard from others that the
defendant intended to find and kill him] went to the
police station and met with a detective. Diaz [disclaimed
his earlier statements to the police and] stated that he
could identify his attacker, whom he called ‘Espana,’
and gave a written statement to the detective. The detec-
tive presented Diaz with an array of eight photographs,
from which Diaz identified . . . the defendant [as the
person who had stabbed him].’’ Id., 725. The defendant
subsequently was arrested and charged with assault in
the first degree, threatening in the second degree, and
interfering with an officer. See footnote 1 of this opinion
and accompanying text.
   On the eve of the defendant’s trial, the assistant state’s
attorney discovered that Diaz, a citizen of the Domini-
can Republic, was not a legal resident of the United
States.3 In addition, over a period of four years, Diaz
had been using the social security card of a United
States citizen named Juan Suarez to obtain more than
$250,000 in treatment for medical problems both related
and unrelated to the injuries that he had sustained from
the stabbing.4 Attorney Aaron Romano was appointed
to advise Diaz of his rights and to counsel him in light
his exposure to prosecution for identity theft and immi-
gration violations. Romano ultimately negotiated an
agreement with the state pursuant to which the state
agreed (1) to grant Diaz immunity from prosecution for
any fraud or identity theft that he may have committed
while impersonating Suarez, (2) not to share any such
information with any other state or federal agency, and
(3) to assist Diaz in obtaining United States citizenship.
In return, Diaz promised to testify truthfully for the
state at the defendant’s trial.
   At trial, William Ramirez testified that, on the night
of February 7, 2008, he was with Diaz near the dumpster
in the alley outside of the market when he heard Diaz
exclaim that he had been stabbed and, immediately
thereafter, saw the defendant run out of the alley with
a knife in his hand. Franklin Ramirez, who was inside
the market when Diaz was stabbed, testified that, after
Diaz was assaulted, he came into the market and stated
that ‘‘Espana’’ had stabbed him. Franklin Ramirez also
testified that, on February 16, 2008, the defendant, who
had returned to the market, stated openly that he had
stabbed Diaz. Diaz testified about the stabbing and the
events leading up to it, and he also made an in-court
identification of the defendant as his assailant. Diaz
also admitted to using a false identity to obtain valuable
medical services; he acknowledged that, under the
express terms of the immunity agreement, his coopera-
tion with the state shielded him from prosecution for
that fraud, and he denied initially informing the police
that he was confronted by two black males.
   Following Diaz’ testimony, the state sought to call
Romano as a witness. According to the state, Romano’s
testimony was relevant because Diaz had been unable
to provide the jury with a coherent explanation about
his agreement with the state, and the state claimed that
Romano’s testimony would assist the jury in under-
standing the nature and scope of that agreement.
Defense counsel objected to Romano’s proffered testi-
mony, claiming that it was irrelevant and would improp-
erly bolster Diaz’ credibility. The trial court overruled
defense counsel’s objection, stating: ‘‘[Romano] can
[testify to] explain [the agreement]. He can’t explain if
[Diaz] is going to testify truthfully, [and] he cannot
bolster the credibility of [Diaz]. . . . [There are] parts
of it that I don’t understand, and [Romano] can explain
those parts. . . . And he can testify that he negotiated
this agreement on behalf of [Diaz] because of the fifth
amendment [to] the [United States] constitution, and
that’s it.’’ Following the ruling, Romano testified about
the purpose of immunity agreements in general and the
details of Diaz’ immunity agreement in particular, as
well as his role in negotiating the agreement for Diaz.
Romano also explained the state’s role in assisting Diaz
to become a United States citizen. In addition, Romano
opined that, when Diaz initially agreed to testify against
the defendant, he did not understand his fifth amend-
ment rights or his potential exposure to criminal prose-
cution arising out of his immigration status and his
incriminating statements to the police concerning his
fraudulent use of Suarez’ identity. Finally, Romano clari-
fied that the assistant state’s attorney retained the right
to determine whether Diaz had fulfilled his obligations
under the agreement and, further, that Diaz would for-
feit the benefits afforded to him under the agreement
if the assistant state’s attorney were to determine that
he had not fulfilled his promise to testify truthfully.
The jury subsequently returned a guilty verdict on the
assault charge.
   On appeal to the Appellate Court, the defendant chal-
lenged his assault conviction on the ground that the trial
court had abused its discretion in permitting Romano to
testify.5 See State v. Rodriguez, supra, 133 Conn. App.
728–32. In support of his contention, the defendant
asserted that Romano’s testimony was both irrelevant
and prejudicial because its sole purpose and effect was
to bolster Diaz’ credibility. See id., 728, 731. The defen-
dant also maintained that, because Romano repre-
sented a witness in the case, the trial court improperly
permitted him to serve as a witness in the absence of
a showing by the state that it had a compelling need
for his testimony.6 See id., 728 n.4. The Appellate Court
rejected the defendant’s claim, concluding that
Romano’s testimony was relevant and not unduly preju-
dicial because his explanation of the purpose and condi-
tions of the immunity agreement aided the jury in
understanding and evaluating Diaz’ testimony in light
of that agreement.7 See id., 731–32. The Appellate Court
declined to consider the defendant’s contention that
the state, in calling Romano as a witness, had failed to
meet the compelling need standard, because the defen-
dant had not raised that claim in the trial court. Id., 728
n.4. The Appellate Court therefore concluded that the
trial court did not abuse its discretion in admitting
Romano’s testimony. See id., 732.
  On appeal to this court following our grant of certifi-
cation to appeal, the defendant renews the claims that
he raised in the Appellate Court. Although Romano’s
testimony clearly was relevant,8 we need not address
the defendant’s other reasons in support of his con-
tention that the testimony was inadmissible because,
even if we assume, without deciding, that the trial court
should have excluded the testimony, its admission
was harmless.
   We turn to the parties’ arguments with respect to
harm. The defendant contends that Romano’s testimony
was prejudicial because it tended to bolster the credibil-
ity of Diaz, who had been impeached extensively with
his admitted identity theft and his initial statement to
the police that he had been confronted by two black
males. The defendant further claims that the trial testi-
mony of the state’s two other key witnesses, William
Ramirez and Franklin Ramirez, was not trustworthy
because they initially failed to provide the police with
the substance of that information despite the opportu-
nity to do so. The defendant argues that Romano’s testi-
mony bolstering Diaz’ version of the events was
important to the state’s case, and therefore was likely
to have affected the outcome of the trial, because the
state’s case rested so heavily on Diaz’ credibility. We
are not persuaded.
   The following well established principles guide our
analysis of the defendant’s claim. ‘‘When an improper
evidentiary ruling is not constitutional in nature, the
defendant bears the burden of demonstrating that the
error was harmful. . . . [A] nonconstitutional error is
harmless when an appellate court has a fair assurance
that the error did not substantially affect the verdict.
. . . [O]ur determination [of whether] the defendant
was harmed by the trial court’s . . . [evidentiary rul-
ing] is guided by the various factors that we have articu-
lated as relevant [to] the inquiry of evidentiary
harmlessness . . . such as the importance of the . . .
testimony in the [state’s] case, whether the testimony
was cumulative, the presence or absence of evidence
corroborating or contradicting the testimony . . . on
material points, the extent of cross-examination other-
wise permitted, and, of course, the overall strength of
the [state’s] case. . . . Most importantly, we must
examine the impact of the evidence on the trier of fact
and the result of the trial.’’ (Citations omitted; internal
quotation marks omitted.) State v. Ritrovato, 280 Conn.
36, 56–57, 905 A.2d 1079 (2006).
   We begin our evaluation with an assessment of the
importance of Romano’s testimony to the state’s case.
We acknowledge, as the defendant asserts, that it is
conceivable that the jury might have misperceived
Romano’s willingness to testify for the state concerning
his representation of Diaz as a general voucher for Diaz’
credibility. Indeed, it may be said that that risk always
exists when a witness’ attorney testifies for the purpose
of explaining the witness’ testimony, especially when,
as ordinarily will be the case, that testimony is corrobo-
rative of the witness’ own testimony. It is also possible
that Romano’s testimony may have served to bolster
Diaz’ credibility with respect to certain specific, albeit
limited, aspects of Diaz’ testimony. For example,
Romano testified that, before he was appointed to rep-
resent Diaz, Diaz did not appreciate the criminal impli-
cations of his admissions about his fraudulent receipt
of medical services. This testimony was consistent with,
and therefore tended to reinforce, Diaz’ assertion that
his decision to testify for the state was motivated by a
desire to see the defendant brought to justice, and not
made for the purpose of securing the benefits granted
to him under the immunity agreement.
  It is apparent, however, that the likely effect of
Romano’s testimony on the jury was minimal. Romano
did not address any ultimate issue in the case, and
at no time did he directly opine on Diaz’ credibility.
Furthermore, in many respects, Romano’s explanation
of the terms, purpose, and effect of the immunity
agreement was no less helpful to the defendant than
to the state. For example, on the basis of Romano’s
testimony concerning the terms of the immunity
agreement, the jury could have concluded that, because
the determination of whether Diaz had testified in
accordance with that agreement rested with the assis-
tant state’s attorney, Diaz had an incentive to curry
favor with the state by falsely implicating the defendant.
Indeed, during closing arguments, defense counsel
urged the jury to reach this very conclusion. In addition,
it was undisputed that Diaz agreed to cooperate with
the state long before Romano was appointed to repre-
sent him and negotiated the immunity agreement on
his behalf. Because this is strong evidence that the
immunity agreement had little if anything to do with
Diaz’ motivation to testify against the defendant, it is
difficult to see how Romano’s testimony about that
agreement had any material bearing on the manner in
which the jury was likely to view Diaz’ testimony.
   Furthermore, Diaz was examined and cross-exam-
ined extensively about his fraudulent use of a social
security card to obtain more than $250,000 in medical
services over an extended period of time, his status
as an illegal alien, and his initial identification of his
assailants as two black males. Moreover, the trial court
expressly instructed the jury that it was entitled to
consider Diaz’ unlawful conduct, stating: ‘‘It is your
duty to determine whether [Diaz] is to be believed
wholly, partly, or not at all. You may consider [Diaz’]
prior misconduct in weighing the credibility of [Diaz]
and give such weight to those facts as you decide is
fair and reasonable in determining the credibility of
[Diaz].’’ Consequently, the jury was aware that, by virtue
of his previous dishonest conduct, Diaz’ integrity and
truthfulness were highly suspect, to say the least.
   Finally, Diaz’ in-court identification of the defendant
as his assailant was corroborated in all respects by
credible, independent evidence. Specifically, William
Ramirez, who was very familiar with the defendant,
testified that he was with Diaz when the assault
occurred and that he observed the defendant fleeing
the scene with a knife in his hand immediately after Diaz
exclaimed that he had been stabbed. Another witness,
Franklin Ramirez, testified that Diaz, after returning to
the market immediately following the assault, told him
that the defendant had stabbed him. Franklin Ramirez
also stated that he had observed the defendant threaten
to harm Diaz earlier that day when Diaz declined to give
the defendant another $20. Finally, Franklin Ramirez
testified that, nine days after the assault on Diaz, the
defendant returned to the market and admitted that he
had stabbed Diaz.
  In sum, this strong, independent evidence that the
defendant stabbed Diaz, coupled with the minimal
import of Romano’s testimony, causes us to conclude
that the defendant cannot establish that the admission
of Romano’s testimony was harmful. Compare State
v. Boyd, 295 Conn. 707, 743–44, 992 A.2d 1071 (2010)
(admission of prior misconduct evidence was harmless
because, inter alia, state’s strong case included testi-
mony from witness who explained defendant’s motive
and stated that defendant had confessed his crime to
her), cert. denied,     U.S.      , 131 S. Ct. 1474, 179 L.
Ed. 2d 314 (2011), and State v. Bonner, 290 Conn. 468,
501, 964 A.2d 73 (2009) (even if trial court improperly
had admitted certain testimony, error was harmless
because state’s case included, inter alia, testimony of
eyewitnesses who had heard defendant confess or who
had observed defendant point gun at victim and flee
scene shortly thereafter), with State v. Finan, 275 Conn.
60, 70–71, 881 A.2d 187 (2005) (harmful error in admit-
ting testimony of four police officers identifying defen-
dant as perpetrator due to substantial weight of
challenged testimony and lack of credible, independent
evidence of defendant’s participation in crime). Accord-
ingly, because the reliability of the verdict is not called
into question by virtue of the trial court’s alleged impro-
priety in admitting Romano’s testimony, the defendant
cannot prevail on his claim that he is entitled to a
new trial.
   The judgment of the Appellate Court is affirmed.
   In this opinion the other justices concurred.
   * The listing of justices reflects their seniority status on this court as of
the date of oral argument.
   1
     In a separate information, the defendant also was charged with threaten-
ing in the second degree in violation of General Statutes § 53a-62 (a) (2),
and interfering with an officer in violation of General Statutes (Rev. to 2007)
§ 53a-167a. The jury found the defendant guilty of these charges, and the
trial court rendered judgment in accordance with the jury’s verdict. The
defendant’s conviction on these charges is not at issue in this appeal.
   2
     The trial court imposed a total effective sentence of sixteen years impris-
onment, execution suspended after eight years, and four years of probation.
   3
     Diaz had been issued a temporary visa permitting his entry into the
United States but had remained here after the expiration of that visa.
   4
     In addition, during the investigation of the stabbing, Diaz identified him-
self to the police as Suarez.
   5
     The defendant also raised a claim of evidentiary insufficiency with
respect to the assault conviction. See State v. Rodriguez, supra, 133 Conn.
App. 724. The Appellate Court rejected this claim; id., 728; which is not at
issue in the present appeal.
   6
     This high bar to admissibility applies to both prosecutors and defense
attorneys in criminal cases. E.g., State v. Peeler, 265 Conn. 460, 474, 828
A.2d 1216 (2003) (‘‘When either side in a criminal case seeks to call as
a witness either a prosecutor or a defense attorney who is or has been
professionally involved in the case, that party must demonstrate that the
testimony is necessary and not merely relevant, and that all other available
sources of comparably probative evidence have been exhausted. . . . This
compelling need test strikes the appropriate balance between, on the one
hand, the need for information and, on the other hand, the potential adverse
effects on the attorney-client relationship and the judicial process in gen-
eral.’’ [Citation omitted; internal quotation marks omitted.]), cert. denied,
541 U.S. 1029, 124 S. Ct. 2094, 158 L. Ed. 2d 710 (2004). The defendant
claimed that the compelling need test also applies to an attorney who, like
Romano, represents a witness in a criminal case.
   7
     More specifically, the Appellate Court explained: ‘‘We are not convinced
that the court committed reversible error in admitting the testimony by
Romano. Because Diaz was testifying pursuant to the immunity agreement,
the jury was entitled to know its terms and the details thereof. Romano
gave detailed testimony as to the purpose and conditions of the immunity
agreement, which was admitted into evidence. Romano testified that his
purpose in representing Diaz was to explain the possible legal ramifications
of Diaz’ testimony at trial—that he could be prosecuted as a result of his
statements admitting to using someone else’s name and social security card
and staying in the United States after his visa had expired—and that he had
sought to minimize any harm to Diaz.
  ‘‘Romano’s testimony concerning his appointment to represent Diaz and
the details of the immunity agreement was [helpful] to the jury’s understand-
ing of Diaz’ presence as a witness and to [its] evaluation of his credibility.
This is especially true in light of the fact that Diaz was examined and cross-
examined extensively about his use of the false identity. Accordingly, we
conclude that the court did not commit reversible error in permitting testi-
mony by Romano.’’ (Footnotes omitted.) State v. Rodriguez, supra, 133
Conn. App. 731–32.
  8
    It is well established that ‘‘[r]elevant evidence is evidence that has a
logical tendency to aid the trier in the determination of an issue. . . . Evi-
dence is relevant if it tends to make the existence or nonexistence of any
other fact more probable or less probable than it would be without such
evidence. . . . To be relevant, the evidence need not exclude all other
possibilities; it is sufficient [for relevancy purposes] if it tends to support
the conclusion [for which it is offered], even to a slight degree.’’ (Internal
quotation marks omitted.) State v. Wilson, 308 Conn. 412, 429, 64 A.3d 91
(2013). Romano’s testimony focused on how and why Diaz’ agreement with
the state emerged, the nature and meaning of that agreement, and Diaz’
understanding of the purpose of and need for the agreement. Romano’s
testimony about those matters was relevant to Diaz’ credibility because the
agreement and Diaz’ understanding of its terms bore directly on any motive,
bias, or interest that Diaz may have had in testifying for the state.
