Limits on Expert Witness Testimony

Dec 6, 2014

The Iowa Supreme Court says expert witnesses cannot testify to a victim's credibility.

Defendants in three recent child sex abuse trials all appealed to the high court, saying expert witness testimony crossed a line. During the trials experts testified, either directly or indirectly, that the children’s behaviors after the alleged abuse were the result of sexual trauma.

The Iowa Supreme Court agreed the testimony went too far. Justice David Wiggins writes, "In our system of justice, it is the jury’s function to determine the credibility of a witness. An abuse of discretion occurs when a court allows such testimony."

Muscatine County Attorney Alan Ostergren is the president-elect of the Iowa County Attorneys Association. Ostergren says often an expert witness, like a psychologist, will explain how certain behaviors children exhibit can be the result of sexual trauma. 

"A child’s grades dropped, that they developed an eating disorder, other behavior changes. And that helps the jury understand what has occurred and connect the dots," say Ostergren. "But the lesson is that the jury has to connect the dots, the expert doesn’t connect the dots." 

So a psychologist might testify children who experience sexual trauma may retreat into themselves, or feel shame. However it's incumbent on other testimony, say from a parent, therapist or teacher, to testify that the child is exhibiting these emotions.  

Only a jury can determine whether the child was abused based on the evidence and testimony presented.