A 20-year-old man has admitted killing four men who went missing a week ago in Pennsylvania, his lawyer says.
"I'm sorry," said a shackled Cosmo DiNardo as he left court on Thursday.
Mr DiNardo allegedly sold the victims cannabis before killing them separately and torching their bodies on his family's farm, local media report.
Investigators found the body of Dean Finocchiaro, 19, who disappeared last Friday, in a "common grave" on the 90-acre farm in suburban Philadelphia.
Officials say there are other remains in the 12.5ft (3.8 metre) deep hole.
Mark Sturgis, 22, and Tom Meo, 21, also vanished on 7 July, and Jimi Tar Patrick, 19, went missing two days earlier.
Local media report that 20-year-old Sean Kratz was taken into custody in Philadelphia on Thursday night as another person-of-interest in the inquiry.
Mr DiNardo killed the four because he felt cheated or threatened during drug transactions, a person with knowledge of his confession told the Associated Press.
He burned the bodies - three of them inside a drum - at his family's farm in Solebury Township, Bucks County, according to local media.
Prosecutors have agreed not to seek the death penalty in return for Mr DiNardo's co-operation, his attorney Paul Lang said outside court.
Officials described the suspect as dangerous and said he has schizophrenia.
The Philadelphia Inquirer reports that Mr DiNardo told fellow members of a Snapchat group that he was not worried about Mr Finocchiaro's whereabouts just days after he had vanished.
'I mean I know the kid but yeah I feel bad for his parents," said Mr DiNardo. "He's a pill-popping junky who had 2 duis… He prob just jumped parole Or probation."
Photos of Mr DiNardo brandishing a pistol have surfaced on the web forum.
The suspect drew suspicion after trying to sell Mr Meo's 1996 Nissan Maxima for $500 (£390), a day after its owner was last seen.
A "life-saving" diabetic kit that Mr Meo requires was still inside the car, investigators said.
A signal from one of the missing men's mobile phones also led investigators to the farmland, according to local media.
District Attorney Matthew Weintraub told a press conference early on Thursday morning: "We had cadaver dogs, and I don't understand the science behind it, but those dogs could smell these poor boys twelve-and-a-half feet below the ground."
Mr Sturgis' father told the Associated Press he had employed his son and Mr Meo, a talented wrestler, in construction, and that Mr Finocchiaro was a mutual friend of theirs.
Mr Patrick and Mr DiNardo both attended the same Catholic boys' high school, a year apart.