Even with photos of his three children in front of him and detectives telling him his family had been "slaughtered," showed almost no emotion as police interviewed him the day of the killings.
In the hours of conversations Vaughn had with Illinois State Police investigators, shown via videotape to a at his murder trial Tuesday, the Oswego man answered questions in a quiet monotone -- even as he was repeatedly accused of lying and of slaying his wife and children.
"I lost everything. Everything that meant anything to me is all gone," Vaughn said at one point.
"And this is your reaction? If it was my kids, I'd be f---ing crying," Special Agent Cornelius Monroe countered.
"Good for you," Vaughn said in an almost inaudible voice.
Kimberly Vaughn, 34, and her children, Abigayle, 12, Cassandra, 11, and Blake, 8, were found inside the family's SUV just before 6 a.m. June 14, 2007. Each child was shot twice; Kimberly Vaughn had a single gun shot wound to the head, fired from beneath her chin.
Prosecutors maintain that Vaughn, now 37, masterminded the deaths of his family to be free of his obligations so he could start a new life in Canada. Defense attorneys say it was a case of murder-suicide, with Kimberly Vaughn shooting her husband, killing her kids and turning the gun on herself.
Only once, late in the proceedings, did Vaughn display any anger. When he pushed away photos of the children, Special Agent Cornelius Monroe pushed them back, prompting Vaughn to stand, crumple one of them and ask if he was under arrest.
"I didn't shoot anybody and I don't have to sit here and listen to this," he said. "I'm not going to talk to someone who's leaning across the table and screaming at me and kicking over chairs."
As quickly as that anger flashed, however, it receded and Vaughn returned to an almost dispassionate demeanor.
The point investigators could not get beyond -- and Vaughn couldn't explain -- was how he came to be shot in the thigh and wrist when he claimed never to have seen or heard a gun, which would have sounded "like a frigging cannon" inside a car, Special Agent Eileen Payonk said. However, only minutes later, Vaughn was telling a good Samaritan who helped him that he thought his wife had shot him.
And, if he didn't think his wife had injured him, why he would seek help on foot rather than using his cell phone or driving away, they asked.
Throughout nearly 14 hours of interviews, which began after Vaughn was treated for gun shot wounds sometime around 10 a.m. June 14, 2007, and didn't end until about 1:30 a.m. June 15, he would not change his story.
"I couldn't think of any reason why I would be bleeding," Vaughn said. "I was going to go for help. I didn't know what was going on. ... I don't know what I was thinking."
He dismissed the idea that he might have intentionally shot himself as "ridiculous," but finally conceded -- when asked to speculate on how he could have come to be shot -- that his wife might have fired a weapon at him.
"All I can think of is somehow Kim got ahold of my gun," Vaughn said. "She (must have) shot me. She shot the kids."
In retrospect, he said he was sorry he didn't stay with his children but he didn't think they were in danger. The decision to leave on foot to seek help was one made out of "panic," he said.
"If you think there's a problem, why wouldn't you stay with your family? Why wouldn't you take them with you?" Monroe asked.
"I don't know," Vaughn responded.
The detectives reviewed many potential reasons Vaughn's wife might have had for wanting to shoot him, including the fact that he'd cheated on her with prostitutes during a business trip to Mexico in late 2006, had a penchant for going to strip clubs and did not spend enough time wth his family.
But there were just as many reasons he might want to escape a marriage he entered into when he 19 and for which, he said, divorce was "not an option." Reasons such a wife who just spent $100,000 for an education and then didn't look for a job using it and who was disinclined to forgive his infidelity even as she nagged about him not being with his family, detectives suggested.
But even presenting Vaughn with a magazine they removed from his home that reportedly contained a story on how to make a murder look like suicide failed to elicit much of a response from Vaughn.
He didn't react when detectives asked if they'd find his fingerprints all over it.
"I never read it," he said.
Here are the stories from the previous days of testimony: