The parents of an American student killed by a quasi-religious cult while on spring break in Mexico said Wednesday their son's killers "must be possessed by the devil."

But James and Helen Kilroy of Santa Fe, Texas, said they believe the "Father in heaven" was caring now for their son, Mark, one of 12 men whose bodies were found buried in shallow graves near Matamoros, Mexico.The 21-year-old pre-medical student at the University of Texas at Austin disappeared March 14 after he became separated from friends who crossed from Brownsville to Matamoros for spring break entertainment.

Authorities said he was killed by members of a drug-smuggling ring that practiced ritual human sacrifice to protect themselves from arrest and even death. Five suspects have been arrested, and authorities searched Wednesday for the group leader, referred to by the others as padrino, or "godfather."

"I think (the suspects) must be possessed by the devil," Helen Kilroy said at a news conference with her husband and son, Keith Kilroy, 19. "That would be the only explanation for such bizarre (actions) and for what they did.

"Now that we've found Mark, we know he's safe," she added. "We know he's with our Lord. . . . Now it's just a matter of all of us - we're going to miss him a lot."

James Kilroy said his son's death showed that even casual drug use can lead to deadly consequences. "So when people stand there next to you and try to tell you that a marijuana cigarette doesn't hurt, they're wrong," he said. "Marijuana is what killed Mark. They were marijuana smugglers."