What information does juror five provide that shows a piece of evidence to be false?

Of the twelve jurors, Juror Five is perhaps the only one who has lived in the slums of New York City. Juror Five's social and economic background gives him a unique perspective on crimes that are similar in nature to the case in question.
Based on his own experiences and what he has witnessed growing up in the housing projects of New York, Juror Five questions the way in which the victim was stabbed. The victim, according to the medical examiner and the prosecutor, was stabbed with a downward motion. However, Juror Five suggests that someone from the slums who is experienced in handling knives would usually stab in an upward motion.
This piece of firsthand information from Juror Five further enhances the rest of the jurors' belief that the prosecution has presented false evidence and that the defendant is not guilty.