Saul Kassin, an expert on false confessions, says coerced confessions are a definite reality in the legal system. "In about 25 percent of the DNA exoneration cases that are out there, there were confessions in evidence as a contributing factor," he says. "And those DNA exoneration cases, those are the lucky few who had DNA in their cases and the DNA was saved and preserved to be tested."
Coerced confessions are more likely to take place when the suspect is young, Saul says, and Marty's naïve nature worked against him. "He'd never been in trouble before. He wasn't street smart. ... He was raised to trust the police," Saul says. "He was in a state of shock and when they brought him in. ... And when they brought him into the station, he wasn't even wearing shoes. He was half-dressed. He didn't have his glasses. He was in a state. That puts him in a state of vulnerability."
Police in Marty's case used his alleged lack of emotion against him, but Saul says there is no one way to react to trauma. "Psychologists who study reactions to trauma know that some people fly into a state of hysteria, but other people shut down, go numb and appear emotionless. That doesn't make them killers," Saul says. "The police are not psychologists in that regard, and to make an inference about somebody being a liar or a truth-teller or a killer or not killer on the basis of whether they're emotional, there's just no evidence for that."
Saul says police lied to Marty numerous times during his interrogation, which he says is legal in the United States. Such lies—including a nonexistent humidity test to "prove" that Marty took a shower after supposedly killing his parents—were used to break Marty down, Saul says. "You can imagine Marty at this point kind of like a boxer who's dazed and weak in the knees about to go down, they lower the boom and McCready goes out and stages a phone call [with Marty's father]," Saul says. "In doing that, he cites to Marty the person in his life he trusts the most. And so Marty breaks down and says, 'If my father says I did it, then I must have done it.'"