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Criminal Jury Instructions

Criminal Jury Instructions Home

2.5-1  Expert Testimony

Revised to December 1, 2007 (modified June 13, 2008)

In this case certain witnesses have taken the stand, given their qualifications and testified as expert witnesses.  A person is qualified to testify as an expert if he or she has special knowledge, skill, experience, training or education sufficient to qualify him or her as an expert on the subject to which the testimony relates.  An expert is permitted not only to testify to facts that he or she personally observed but also to state an opinion about certain circumstances.  This is allowed because an expert, from experience, research and study, generally has a particular knowledge of the subject of the inquiry and is more capable than a lay person of drawing conclusions from facts and basing an opinion upon them.

[<If hypotheticals were used:>1  An expert witness may state an opinion in response to a hypothetical question, and some experts have done so in this case.  A hypothetical question is one in which the witness is asked to assume that certain facts are true and to give an opinion based on those assumptions.  The value of the opinion given by an expert in response to a hypothetical question depends upon the relevance, validity and completeness of the facts he or she was asked to assume.  The weight that you give to the opinion of an expert will depend on whether you find that the facts assumed were proved and whether the facts relied on in reaching the opinion were complete or whether material facts were omitted or not considered.  Like all other evidence, an expert's answer to a hypothetical question may be accepted or rejected, in whole or in part, according to your best judgment.]

Allowing someone to give expert testimony is in no way an endorsement by the court of the testimony or the credentials of the witness.

Such testimony is presented to you to assist you in your deliberations.  No such testimony is binding upon you, and you may disregard the testimony either in whole or in part.  It is for you to consider the testimony with the other circumstances in the case, and, using your best judgment, determine whether you will give any weight to it, and, if so, what weight you will give to it.  The testimony is entitled to such weight as you find the expert's qualifications in his or her field entitle it to receive, and it must be considered by you, but it is not controlling upon your judgment. You are also to consider his or her general credibility in accordance with the instruction on credibility applicable to all witnesses.

In this case you were provided expert testimony by the following witnesses: <list the expert witnesses>.

1  See State v. Michael G., 107 Conn. App. 562, 570 , cert. denied, 287 Conn. 924 (2008) (finding error in court's failure to give requested charge on the factual basis of an expert's opinion based on a hypothetical question).


A proper instruction on expert testimony directs the jury to evaluate the testimony by the same standards as ordinary witnesses.  State v. Borelli, 227 Conn. 153, 174 (1993); State v. Harvey, 27 Conn. App. 171, 188-89, cert. denied, 222 Conn. 907 (1992).

It is permissible for experts who testify as to the "typical reaction to physical and sexual assault trauma" to answer hypotheticals about whether certain conduct would be consistent with such trauma.  State v. Freeney, 228 Conn. 582 (1994); State v. Niemeyer, 55 Conn. App. 447 (1999), rev'd in part on other grounds, 258 Conn. 510 (2001).  This type of testimony does not invade the province of the jury in determining the credibility of the victim.  Niemeyer specifically rejects the suggestion that the dissenting opinion in Freeney in any way requires a more extensive instruction on the issue.  See also State v. Russo, 38 Conn. Sup. 426 (App. Sess. 1982) (court properly instructed the jury that they must reject the opinion of an expert witness to the extent that it is based on subordinate facts which the jury does not find proved, though the court should specifically delineate these subordinate facts).

See generally General Statutes 54-86i; Code of Evidence 7-2, 7-3, and 7-4.  Section 7-3 (a) of the Code of Evidence prohibits opinion testimony on an "ultimate issue," unless the fact finder "needs expert assistance in deciding the issue."  However, 7-3 (b), which incorporates the language of General Statutes 54-86i, limits this exception in criminal cases, prohibiting experts from testifying as to whether the defendant had the requisite mental state for the alleged crime.  "The ultimate issue as to whether the defendant was criminally responsible for the crime charged is a matter for the trier of fact alone."  Id.  See also State v. Finan, 275 Conn. 60, 66-69 (2005) (the identification of the defendant as one of the perpetrators shown on a security videotape was an ultimate issue).


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