In their first public interview since attacking gay college student Matthew Shepard (search), his killers said they were motivated not by homophobia, but the prospect of robbery to fuel a methamphetamine binge.

"He was pretty well-dressed, had a wallet full of money," Aaron McKinney (search) said of meeting Shepard at a Laramie bar in October 1998. "All I wanted to do was beat him up and rob him. ... Seemed like a good idea at the time."

The interviews air Friday on ABC's "20/20."

The robbery got out of hand, said McKinney and his buddy, Russell Henderson (search), and Shepard was beaten into a coma while tied to a fence outside the small college town. The 21-year-old died five days later.

The crime drew condemnation from President Clinton, Congress and the international community, and spurred debate on the effectiveness of hate crime laws. McKinney and Henderson, both 27, are serving life sentences for murder.

McKinney said he killed Shepard because he was strung out on drugs, not because Shepard was gay. Henderson agreed, saying "it's not because me and Aaron had anything against gays or any of that."

Henderson said that McKinney, who had been bingeing on meth for days, set out that night to rob a dealer of $10,000 worth of the drug. Henderson thought if he could keep McKinney drinking, his friend would forget the plan.

McKinney said Shepard was sitting at the bar when he and Henderson arrived, and at one point McKinney asked Shepard for a cigarette.

"He said he was too drunk to go home and then he asked me if I'd give him a ride," McKinney said.

In the truck, McKinney claimed, the two learned Shepard wanted sex in return for giving them drugs, but McKinney decided to rob Shepard instead.

According to McKinney, Shepard grabbed his leg and he struck Shepard with his gun and demanded money. Although Shepard handed over his wallet, the beating continued.

"Sometimes when you have that rage going through you, there's no stopping it," McKinney said. "I've attacked my best friends coming off of meth binges."

They decided to dump Shepard in a secluded spot, and when they came upon a rustic fence blocking the road, McKinney decided to tie him to it.

"Then when I'm leaving, he says he's going to tell on me," McKinney said. "I went back and hit him one more time. I hit him real hard that time."

One of McKinney's attorneys, Dion Custis, said Wednesday that drugs and robbery, not sexuality, have long been considered the main motives for the crime.

"If anyone saw the trial and the evidence that was presented at trial, that was exactly what we presented at the time," he said.

Prosecutor Cal Rerucha also said the case was too complex to simply be labeled a hate crime. He said many people overlooked the drug and robbery aspects of the case at the time of the attack.

"People want an easy answer to this case and I don't think we would be here five years later if there was an easy answer," Rerucha said.