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The Molineux Rule And The Scope Of Expert Witness Testimony

People v. Rivers 2011 NY Slip Op 08455 

Decided November 22, 2011 New York Court of Appeals 

See also Eyewitness Identification Expert: When Is Expert Testimony Admissible


1) Whether repeated violations of the trial court’s Molineux ruling was so prejudicial that it warranted a new trial;

2) Whether the scope of the expert testimony that ruled out accidental and natural causes of the fires and concluded that the fire was set intentionally invaded the jury’s province


1) The evidence that was improperly admitted in violation of the court’s Molineux ruling was subject to harmless error analysis and because there was overwhelming proof of guilt there was no reasonable possibility or significant probability that the improper questions and elicited references to defendant’s bad acts and negative associations affected the jury’s verdict.

2) The admission of the expert’s testimony was also subject to harmless error analysis and the Court of Appeals held that the guiding principle to admitting expert opinion is that it is properly admitted when it would help clarify an issue calling for professional or technical knowledge, possessed by the expert and beyond the ken of the typical juror and this principle applies to testimony regarding both the ultimate questions and those of lesser significance.  The testimony was admissible because there was additional evidence adduced at trial that demonstrated that the fires were set intentionally.

Facts: Defendant was charged with numerous offenses, including three counts of arson in the first degree in connection with two fires set five days apart in a four-story apartment building located at 408 Greene Avenue in Brooklyn, New York.

On appeal, defendant argued that the prosecutor repeatedly violated the trial court’s Molineux rulings by eliciting evidence of an uncharged arson attempt and of his prior bad acts and associations — the elicited testimony linked defendant to violence, guns, the Nation of Islam, and a violent motor cycle gang.

During the course of the trial testimony was elicited from an expert witness that ruled out accidental and natural causes of the fires and concluded that one of the fires was intentionally set.  The defendant argued on appeal that this invaded the province of the jury and was improperly admitted.

Legal Analysis: To the extent any evidence subject to the trial court’s Molineux rulings was improperly admitted, such error was harmless.  The evidence against defendant, from his own taped admissions, and testimony of the individual who set the first fire at defendant’s behest, overwhelmingly established defendant’s guilt of the crimes charged.

Further, there was no reasonable possibility or significant probability that the improper questions and elicited references to defendant’s bad acts and negative associations affected the jury’s verdict, or that the absence of such errors would have led to an acquittal.

New York has a well-established body of case law concerning the admissibility and limits of expert testimony, that should be brought to bear in deciding what an arson expert may tell the jury in a particular case. “The guiding principle is that expert opinion is proper when it would help to clarify an issue calling for professional or technical knowledge, possessed by the expert and beyond the ken of the typical juror”  Moreover, this principle applies to testimony regarding both “the ultimate questions and those of lesser significance”

Although, in deciding whether expert testimony is admissible, courts must determine whether “the potential value of the evidence is outweighed by the possibility of undue prejudice to the defendant or interference with the province of the jury”.

“Courts should be wary not to exclude such testimony merely because, to some degree, it invades the jury’s province”. “Expert opinion testimony is used in partial substitution for the jury’s otherwise exclusive province which is to draw ‘conclusions from the facts.’ It is a kind of authorized encroachment in that respect”   Obviously, expert testimony would not generally be admissible in a case where the fire’s cause is not in question.

Here, because the evidence adduced at trial conclusively established, apart from the expert testimony, that the subject fires were intentionally set, it can be argued that the admission of expert testimony was largely unnecessary. In any event, any error was harmless, because the evidence of defendant’s guilt was overwhelming and there was no significant probability that the jury would have acquitted defendant without the expert testimony.