Imagine You Are Asked to Testify at a Grand Jury

Imagine you are asked to testify at a grand jury, by the defense, as an expert on eyewitness memory. The defendant is charged with armed robbery and the prosecution has presented a witness who says that shortly after the crime was committed, she saw the defendant running down the street with a bag in his hands. What would you tell the jury about the accuracy of eyewitness memory in your testimony?