Disclaimer - the facts of this case allege a child rape.
The New York Court of Appeals just decided a case last week that explains what happens when a prosecutor uncovers their error in the middle of trial and tries to correct it in People v. Kelley,
It was a sexual assault case, a father raping his daughter. The police collected the victim's underwear, bedsheets, and a towel that was supposedly used for the defendant's semen. The underwear contained male DNA, but it wasn't the defendant's DNA. It was an unknown male.
The prosecution was going to trial without testing the towel. It appeared to just be an oversight. Either the prosecutor didn't know the towel existed, thought it was already tested for DNA, or forgot about it. So the defense at trial was that yes the girl was raped, but it wasn't the defendant. Look at the DNA on the underwear. It's not his and that shows he's innocent.
During the trial, the prosecutor had the towel tested. The results came back after the defense attorney put forth his defense and the defendant testified. The towel contained semen and the DNA matched the defendant's DNA. But the female DNA on the towel wasn't the victim's. Now there was corroboration for the victim's version of events. And the defense theory of the case? This blew it out of the water.
The trial judge allowed the evidence into trial over the defense objection that his client's right to a fair trial was impaired. The defendant was convicted and appealed. The Court of Appeals reversed. They said that the proper ruling should have been to preclude the evidence at trial or to declare a mistrial and start over. The defense theory of the case was irreparably harmed due to allowing the evidence in the middle of the trial. The trial was too far along to call it a harmless error.
One Justice dissented, stating that the trial court acted property because the late testing was not a deliberate strategic act, but a simple oversight.
It doesn't matter though, because the Court of Appeals has spoken and the case must be retried. The daughter must testify against her father again in Court.
I empathize with the prosecutor. Every one of us makes mistakes that affect a case. We're human. It's a difficult phone call to make to a sexual assault victim. The call that she has to go through it again.