The other man, Cosmo Dinardo, had a dark, grisly secret, police say.
Sean Kratz is charged in the deaths of Dean Finocchiaro, 19, Thomas Meo, 21, and Mark Sturgis, 22.
During a news conference, it was revealed that DiNardo's confession led to the location of the four bodies and the implication of Mr. Kratz in the crime. He said locating Patrick's body on the 80-acre property independently would have been very hard.
DiNardo's lawyer said his client confessed to the murders in exchange for prosecutors agreeing to not seek the death penalty.
"We have the two men locked up that need to be brought to justice", Weintraub said. "We will not rest until we do that".
Weintraub said DiNardo's confession provided "valuable intelligence and information" that enabled them to charge Kratz. He said Dinardo led authorities to the fourth body.
"They've done nothing to deserve this frightful, unspeakable tragedy that has been set upon them", Weintraub said of the families at a news conference Friday, adding that they handled the uncertainty with dignity and courage. "I'd like to think that he wanted to help us get the boys home".
On Thursday, DiNardo broke silence and confessed to selling the four men marijuana, before killing them on the farm, according to the Associated Press. He says Patrick only had $800 so he offered to sell him a shotgun instead; then he shot him.
Patrick's body was discovered in a six-foot deep hole in a remote area on the DiNardo family property. DiNardo, of Bensalem, is charged with four counts each of criminal homicide; Kratz, of Philadelphia, is charged with three counts each of homicide.More news: De Mistura: Direct Syrian Talks in Upcoming Rounds
When the prosecutor held a dramatic midnight Wednesday news conference to announce the discovery of remains, Claire Vandenberg, of neighboring New Hope, gathered around a TV with a group of friends to hear developments on what she said is "all we talk about". However, Kratz told police that Dinardo was the one who shot Finocchiaro. Dinardo told police that he shot Meo in the back, and as Sturgis started to run away, Dinardo shot Sturgis, killing him.
Kratz alleges that DiNardo shot Finocchiaro, the affidavit said.
DiNardo was arrested earlier this week on charges stemming from the investigation.
Patrick and Cosmo Dinardo, whose parents own the farmland, graduated from Holy Ghost Preparatory School a year apart from each other, school spokesman Bill Doherty said.
That same night, DiNardo said, he met Meo and Sturgis together at a parking lot in Peddlers Village.
The two then placed the bodies of Meo and Sturgis in the same metal tank as Finocchiaro, records show.
Dinardo told investigators he then poured gasoline and lit the tank, according to the affidavit. He then "ran over Meo with the backhoe", before using it to dump the bodies into a metal tank where they would join Finnocchiaro. Rather that "there was an attempt to burn the bodies" but that it "was not successful".
While Kratz says Finocchiaro was also killed during what was supposed to be a marijuana deal on July 5, DiNardo says this murder occurred on July 7. "I'm not sure I could ever answer that question", Weintraub said, according to the Philadelphia Inquirer. Both young men did not go to work on Saturday, police said. The body was later found Thursday by investigators. He displayed a bouquet of flowers - sent by a member of the community - that he meant to distribute to as many law enforcement officers as possible.
He wrote on Snapchat: "I mean I know the kid but yeah I feel bad for his parents".