family's farm, a person with firsthand knowledge of his confession said.
The person spoke to The Associated Press on the condition of anonymity on Thursday because he was not authorized to publicly discuss details of the case against 20-year-old Cosmo DiNardo, who was in custody.
DiNardo told authorities that a co-conspirator from Philadelphia was involved in three of the deaths, the person said.
The details were provided after one of DiNardo's lawyers said Thursday that DiNardo had confessed to killing the missing suburban Philadelphia men and told investigators where their bodies were located. DiNardo agreed to plead guilty to four first-degree murder counts, attorney Paul Lang said.
In exchange for DiNardo's cooperation, Lang said, prosecutors would not seek the death penalty.
The Bucks County district attorney didn't comment on the case Thursday night, though his office did tweet news reports of DiNardo's confession. Authorities were expected to release additional information Friday.
The person with knowledge of the confession said one of the men was killed July 5 and the other three were killed July 7.
"Every death was related to a purported drug transaction, and at the end of each one there's a killing," the person said.
DiNardo, 20, then burned the bodies — three of them inside a drum — at his family's farm in Solebury Township, about 30 miles (48 kilometers) north of Philadelphia, the person said.
As a law enforcement official escorted a shackled DiNardo from the courthouse on Thursday, he said "I'm sorry." His parents declined to comment after leaving a government building where he spent several hours with investigators.
Authorities had charged DiNardo earlier this year with having a gun despite an involuntary mental health commitment. In seeking $5 million bail on a stolen car charge this week, prosecutors said he had been diagnosed with schizophrenia. He also suffered a head injury in an ATV accident a year ago.
The victims are 19-year-old Dean Finocchiaro, 22-year-old Mark Sturgis, 21-year-old Tom Meo and 19-year-old Jimi Taro Patrick. Patrick, who was a year behind DiNardo at a Catholic high school, was last seen on Wednesday, while the other three vanished two days later.
Cadaver dogs led investigators this week to the spot on the family farm where they discovered human remains inside a 12 ½-foot-deep common grave. So far, investigators said they have only been able to identify one set of remains — those of Finocchiaro.