ATLANTA - Georgia prosecutors said Wednesday they are searching for more suspects in the killing of an 18-year-old who was stomped to death in an apparently random attack at a house party over the weekend, even as three of the four men charged with the teen's murder say they are innocent.

Douglas County District Attorney David McDade said witnesses have indicated there may have been others involved in the death of Bobby Tillman, who was stomped, kicked and punched to death early Sunday at a house party while dozens of bystanders watched.

"With so many young people in the crowd you can imagine the difficulty we are having in sorting out the numerous varying versions of what took place," McDade said. "We are working on identifying everyone involved if we can."

Tillman and about 80 others had descended on a house party Saturday night in Douglasville, a working-class suburb west of Atlanta, that spilled out on the street when the crowd grew unruly. Then authorities say a fight broke out and a woman hit one of the male partygoers.

In a perverted sense of chivalry, the man decided not to retaliate against her because she was female, authorities said. But they said he vowed to strike back against the next man who passed by. That happened to be Tillman, whose friends say he was in the wrong place at the wrong time.

Authorities say at least four teenagers assaulted him, hitting him so hard that his heart was cut during the beating. Witnesses said they saw Tillman stand briefly after the attack, only to stumble to the ground again. He was still breathing when rescuers arrived, but died minutes later.

Four men were charged with murder in the killing. They are Quantez Devonta Mallory, 18; Horace Damon Coleman, 19; Emanuel Benjamin Boykins, 18; and Tracen Lamar Franklin, 19. Franklin, Boykins and Coleman told television reporters Tuesday at the jail they were innocent, while Mallory declined to be interviewed.

Tillman's mother, Monique Rivarde, said she had faith in the district attorney's investigation.

"We're just looking for justice," she said. "I just want justice for my son and I have full trust in the district attorney. If he arrests more people, then so be it."

She said she would not comment on whether prosecutors should pursue the death penalty against any of the suspects, who could be indicted within two weeks. And McDade said it's still too early to tell whether he'll recommend capital punishment in the case.

"I certainly want the investigation to be completed before I make any decisions and of course I will need to spend a great deal of time with the victim's family discussing the various options before I make any decisions," he said.