A cannabis dealer has given police a gruesome account of killing four men on his family's US farm, saying he crushed one of them with a digger after shooting him and tried to set three of the bodies on fire in a metal bin, court papers show.
Cosmo DiNardo, 20, said he killed a former schoolmate in Pennsylvania when he arrived with 800 US dollars to buy 8,000 dollars worth of drugs.
He said he shot another man in the back as he tried to run away.
DiNardo blamed one of the deaths on a cousin, Sean Kratz, who was also charged on Friday over the case.
Kratz, 20, told police that DiNardo shot all four of the victims.
"I'm sorry," DiNardo, who graduated from a Catholic prep school two years ago, said on Thursday as he was led into a police van.
The only motive investigators have mentioned was that DiNardo said he wanted to set the victims up when they came to the farm to buy marijuana.
One man vanished on July 5 and the others two days later. Three of the slain men were buried at the farm in an oil tank that had been converted into a cooker.
The FBI found them on Wednesday after four days of methodical hand-digging and sifting in a spot on the 90-acre farm that dogs had identified.
Authorities might never have found the fourth body unless they worked with DiNardo, Bucks County District Attorney Matthew Weintraub said.
"I don't know what convinced him (to confess). I'd like to think he wanted to get these boys home," he said, explaining the surprise plea agreement forged on Thursday that led them to the final body.
DiNardo told police where to find 19-year-old Loyola University of Maryland student Jimi Taro Patrick, and agreed to plead guilty to four counts of first-degree murder.
In exchange, he will be spared the death penalty.
The other victims are 19-year-old Dean Finocchiaro, 22-year-old Mark Sturgis and 21-year-old Tom Meo. Mr Patrick was a year behind DiNardo at Holy Ghost Prep School near Bensalem.
"We'd still be looking for Jimi Patrick had we not made this agreement," Mr Weintraub said. "It was so far away (from the others on the farm) that I started to get sick to my stomach on the ride."
DiNardo's history of mental illness includes an involuntary commitment, a schizophrenia diagnosis and repeated contacts with police. He also suffered a head injury last year in an quad bike accident.
The commitment meant he was barred from possessing guns, but he had one in February when police charged him with having a shotgun.
He also used at least two guns in the killings, investigators said.
A source with knowledge of his confession said he acknowledged selling a variety of handguns to local residents.
DiNardo is charged with four homicide counts and 20 other crimes, including abuse of a corpse, conspiracy and robbery.
Kratz faces 20 counts, including three of homicide. Both are being held in jail without bail.
DiNardo's parents, who own the farm in Solebury as well as construction and concrete companies in Bensalem, where they live, declined to comment as they left a court after their son confessed.
Kratz's mother, Vanessa, declined to comment on her son's arrest.