McKinney says he asked for, and got, Shepard's wallet, which had only $30 in it. But even though Shepard handed over his money, McKinney continued beating him.
When pressed by Vargas as to why he continued beating Shepard after he had already taken his wallet, McKinney said, "Sometimes when you have that kind of rage going through you, there's no stopping it. I've attacked my best friends coming off of meth binges."
McKinney says he directed Henderson to drive the truck to a secluded spot on the outskirts of Laramie so they could leave Shepard and have time to get away. They stopped at a wooden buck fence and took Shepard from the truck.
On McKinney's instructions, Henderson got a rope from the truck and tied Shepard to a fence post. Henderson claims at some point he tried, but failed, to stop McKinney from beating Shepard further.
In a statement to the court, Henderson said McKinney struck him across the face with the gun when he tried to stop the continued beating of Shepard.
Henderson retreated to the truck, leaving McKinney alone with Shepard at the fence. McKinney tells "20/20" he fears these last blows he dealt Shepard at the fence were the fatal blows.
McKinney took Shepard's wallet and his shoes, got back in the truck and told Henderson to drive to town. He says his plan was to burglarize Shepard's apartment. But when they parked the truck they encountered two young men who police say were vandalizing cars. Hostile words led to a fight and for the second time that night, McKinney went on the attack.
One of the men was struck so hard his skull was fractured. The injured man's friend retaliated, slamming McKinney in the head with a small bat. Everyone fled, just before a police car happened on the scene.
Sgt. Flint Waters gave chase and grabbed Henderson. Then he discovered some key evidence that would later be used to link Henderson and McKinney to the attack on Shepard.
"I looked in the back of the truck and laying in the back of the truck was a large-frame revolver. The thing was huge, like an 8-inch barrel that had blood all over it. And there was some rope and a coat in the truck; there was I believe a shoe sitting in the front. ... Seeing that the gun covered in blood, I assumed that there was a lot more going on than what we'd stumbled onto so far," he said.
With that much evidence and McKinney's later confession, the attack on Shepard was not a hard case to solve. McKinney and Henderson were charged with murder. The mystery in this story was not who did it, but why?
Just hours after Shepard's battered body was discovered, and before anyone knew who had beaten him, Shepard's friends Walt Boulden and Alex Trout began spreading the word that Shepard was openly gay and that they were concerned the attack may have been a gay-bashing.
Boulden told "20/20" in an interview shortly after the attack in 1998, "I know in the core of my heart it happened because he revealed he was gay. And it's chilling. They targeted him because he was gay."
Prosecutor Rerucha recalls that Shepard's friends also contacted his office. Rerucha told "20/20," "They were calling the County Attorney's office, they were calling the media and indicating Matthew Shepard is gay and we don't want the fact that he is gay to go unnoticed."