While some of Mermel’s tactics have drawn the ire of defense lawyers, others give him grudging respect for his skill in the courtroom. “He’s a very effective trial lawyer,” Stone said. “But his view of the world is very narrow.” In the case of Juan Rivera, Lake County prosecutors have been able to convince juries, not once but three times, that he was the murderer, despite DNA evidence in the last trial that powerfully suggested otherwise. (Mermel was the lead lawyer on the third trial and assisted in the second.)

“We don’t fold our tents and run,” Mermel told me when we spoke this spring. “We don’t quaver because somebody holds up three letters: DNA.”

When I asked him specifically about the Rivera case, Mermel said that sometimes post-conviction evidence is irrelevant. “The example I like to give people is next time you go to a motel room, bring a plastic bag, because the dirtiest thing in that room is the remote control. Everybody has sex and then rolls over and goes, ‘I wonder what’s on?’ ” he said. “O.K., so you can find DNA in the form of sperm from 10 different people in that room from that remote control or even on a person who has touched it. And that woman gets murdered in that room tonight, and you are going to have a lot of DNA. Is it all going to be forensically significant?”

His theory for why there was sperm that did not come from Juan Rivera inside 11-year-old Holly Staker on the day she was murdered is, to his mind, simple and straightforward. She and her twin sister, Heather, were sexually active, Mermel argues, and Holly must have had sex with someone else before Rivera came along and raped (but didn’t ejaculate) and murdered her. There was scant evidence to support this sexual-activity theory, but Mermel dismissed that objection. “Nobody is going to admit to having sex with an 11-year-old girl, even if the statute of limitations has run out,” he told me. “But there was a lot of evidence that came to our office that these two girls were sexually active.”

When a DNA test in 2003 showed that the semen in the underwear of a 68-year-old woman didn’t belong to Bernie Starks, a man convicted in 1986 of raping and murdering her, Mermel dismissed the results because the semen came from the victim’s clothing. Had it come from the woman’s vagina, Mermel said, “I would be standing over there advocating the side that the defense has in the case.”

Three years later, defense attorneys found the rape kit and tested semen recovered from the woman’s vagina. Again, there was no match. Mermel again wouldn’t budge, this time arguing that the woman must have had sex with someone else just before the rape.

Mermel’s biggest blunder was Jerry Hobbs, who was arrested in 2005 on charges of raping and stabbing to death his 8-year-old daughter and her 9-year-old friend. Hobbs confessed to the killings, but only after 16 straight hours of questioning that began after he’d spent the previous night looking for the girls….

When Hobbs’ attorneys revealed in court in 2008 that DNA tests showed the semen found in the mouth, rectum, and vagina of Hobbs’ daughter didn’t belong to Hobbs, Mermel postulated that the foreign semen must have found its way into the girl’s body while she was playing in a patch of woods where teenagers were known to have sex. The girl had been found fully clothed.

When Lou Tessmann retired from the Waukegan police in 2005, the Illinois House of Representatives passed a resolution praising his two decades of service. The resolution noted that Tessmann, a former Marine, is “well known for his interrogation techniques on suspects of crimes.”

Since then, Tessmann has traveled the country offering seminars to police officers on how to investigate homicides and interrogate potential suspects. “Mr. Tessmann has obtained over 80 homicide confessions during his career with only three instances where he was unable to obtain a confession from a homicide suspect” — a 96 percent success rate — according to the Web site of his employer, Wicklander-Zulawski & Associates.

It was Tessmann who was sent in to interrogate Rivera around 11:30 a.m. on Oct. 30, along with Sgt. Michael Maley of the Illinois State Police. In the hour or two before the interview began, Rivera was hitting his head against a glass window and was then on the floor with his wrists and ankles cuffed behind him. Tessmann, however, described Rivera as “very comfortable, very relaxed” during the interview.

Though Tessmann arrived at the police station roughly seven hours before the interview, he testified that he wasn’t aware of Rivera’s previous confession. (One of his colleagues testified that he gave Tessmann the statement that morning.) He said that Rivera willingly recounted the crime, which then cleared up many of the issues that prosecutors considered problematic.

In his closing argument in the third trial, Mermel told jurors that the case basically came down to whom they believed: the police or the DNA evidence? “Is there anything in the makeup of any of those men that would lead you to believe that they were the kind of people who had dedicated their lives to this profession, yet just decided to just frame this poor innocent Juan Rivera because they were tired of investigating and wanted to go home?” he said.

What the jury didn’t know was that Mermel had already successfully argued against the admissibility of any evidence that might cast doubt on Tessmann’s credibility. For instance, Tessmann said in a 1990 deposition and in an official biography that he earned an English degree from the University of Wisconsin. But the school’s 13 four-year colleges have no record of him ever attending. (In fact, he graduated from Northeastern Illinois University.) In 1989, Tessmann and four other police officers were sued for allegedly breaking into the wrong home during a police raid and injuring a woman who was seven months pregnant. The woman’s lawyer accused the police of writing reports to cover up their conduct and charged that Tessmann “took the lead in creative drama.”

According to documents provided by defense lawyers, a judgment was entered against Tessmann and the other officers for $48,500 in that case, and two years later, another judgment of $71,500 was entered against Tessmann in a case brought against him by a man who was wrongfully arrested for robbery.

A decade later, in 2001, a woman named Colleen Blue was charged with murder after she confessed to killing her newborn. Tessmann, then a commander, said to a reporter for The Chicago Daily Herald, “She told us she had six kids already and just did not want to deal with another one.” He added: “She said she gave birth to the baby when she was all alone, put him in the bag and walked off. She told us she could hear the baby crying until she got close enough to the street that the passing cars drowned out the sound.”

Charges against Blue were dropped when DNA testing revealed it wasn’t her baby.