The next day, police picked up Sanford again and interrogated him. The second session was not recorded, and the only evidence of what happened is a final statement the officer typed. This time, Sanford said he and three friends met at a park (not a restaurant) and his description of the guns matched those used in the killings. In Sanford’s third interrogation, he said two friends drove away in a van (a different vehicle than in the first and second confessions) and that he and an accomplice ran away from the house—an account that would match what witnesses said they saw.

Eventually, officers would say Sanford described where the bodies lay in the house, something only the killer would know.

“The way the interrogation process is set up in this country is that it’s designed not to get information from you, but to get a confessions,” Trainum, the former Washington D.C., detective told me. “I’m only supposed to interrogate people who are guilty. I’m supposed to ask you things as if I knew without a doubt in my mind you are guilty.”

Two years ago, in Police Chief Magazine, Trainum wrote an article that outlines how an innocent person under interrogation can willfully admit to a crime (s)he didn’t commit. First, interrogations are high pressure. An officer might ask 30 questions, Trainum said, and get 29 wrong answers, but what counts is the one that’s right—or close. Next, police can lie. They can tell a suspect they have their fingerprints, or witnesses putting them at the crime scene, or DNA that matches—moves intended to put suspects on the defensive and get them to reveal details about the crime that no one but the criminal would know. But this second approach involves officers letting important details slip out—deliberately or accidentally—during interrogation; details known only to the police and the culprit.

The suspect, in this case Sanford, under a barrage of questioning feels compelled to confess to a crime he didn’t commit.

“Basically, we create a situation where you are faced with what you perceive to be an inevitable consequence,” Trainum said, placing himself in the suspect’s position. “He’s telling me, ‘I have all this evidence and they have these witnesses. He’s telling me I’m going to be found guilty no matter what. I’m screwed. But he’s also telling me that if I confess he’s going to help me. I can go home. That this will go away. I just need to tell him what he wants to hear.”

In fact, it was a false confession that Trainum owes to his current path of educating officers on correct interrogation techniques. In 1994, he worked a case where someone had been bound, beaten to death, then dumped in D.C.’s Anacostia River. His main suspect was a 19-year-old homeless woman, who confessed after a 17-hour interrogation. The District later dropped the charges, because it couldn’t have been her. So why then, Trainum wondered, had she confessed? When he listened to the recording of the interrogation, he heard himself accidentally pointing her toward answers, revealing the hold-back information only the murderer––and police––could have known. When she parroted this back in conversation, it seemed like she must be the murderer. The reason he was so blinded, he said, was because most officers are taught an interrogation is supposed to elicit a confession, not to learn about the case.