The criminal-justice system in Lake County, Illinois is coming under increasing scrutiny. It’s not just the DNA exonerations. It’s that even when post-conviction testing of DNA evidence disproves the prosecution’s case, the District Attorney, Mike Mermel, still believes that his team of prosecutors has gotten the right guy. Mr. Mermel appears to suffer from god complex. So what if DNA evidence proves that the defendant was not the source of the semen left by the perpetrator? Rather than admit that his office might have made a mistake and that there is reasonable doubt, Mr. Mermel comes up with all kinds of logical contortions and hypotheses just to support the verdict.

(My favorite, a man was convicted of killing a nine-year-old girl in the woods. DNA testing done after his trial discovered that there was sperm in the mouth, vagina, and anus of the stabbing victim. The sperm did not come from the defendant. Mr. Mermel supposed the sperm came from the girl playing in the woods, where people have had sex.)

Mr. Mermel dismisses his skeptics with a wink, saying “the taxpayers don’t pay us for intellectual curiosity. They pay us to get convictions.” Wrong. The Supreme Court has stated: “The [prosecutor] is the representative not of an ordinary party to a controversy, but of a sovereignty whose obligation to govern impartially is as compelling as its obligation to govern at all; and whose interest, therefore, in a criminal prosecution is not that it shall win a case, but that justice shall be done. As such, he is in a peculiar and very definite sense the servant of the law, the twofold aim of which is that guilt shall not escape or innocence suffer.” Put another way, the duty of a prosecutor is not just to convict the guilty but to spare the innocent.