A recent Michigan Court of Appeals panel reversed a conviction for Criminal Sexual Conduct First Degree, commonly called rape, due to improper witness vouching. The case involved three expert witnesses, all of whom testified for the government. In different and sometimes subtle ways, each expert made improper statements about the complaining witnesses (CW) credibility that amounted to their “vouching” for the CW’s credibility.
According to the standard jury instructions utilized in Michigan sex crimes cases it is up to the jury to judge and weigh a witness’s credibility. In reaching this determination, the jury will be instructed to consider a variety of factors including how well the witness was able to see and hear things and was there anything that might have distracted them; how good is their memory; how do they look and act while testifying and do they seem to be telling the truth or are they trying to evade answering and arguing with the lawyers, do they have any personal interest in how the case is decided, and how reasonable is their testimony when compared with all of the other evidence in the case. See M Crim JI 2.6.
Notice that “what do other people think about the witness’s credibility” is not among the factors for the jury to consider. Vouching is improper therefore because it “invades the province” of the jury by substituting someone else’s opinion for the jury’s collective determination.