Four young men who disappeared from Bucks County last week were lured to their deaths with promises of being sold pounds of marijuana, only to be executed by a pair of cousins who later disposed of their bodies in gruesome fashion.

Cosmo DiNardo, 20, an admitted drug dealer with a history of mental illness, was charged Friday with the killings of the four Pennsylvania men. He faces 20 additional counts, including abuse of corpse, conspiracy and robbery.

A second 20-year-old suspect, Sean Kratz, was also arrested and faces 20 counts in three of the deaths.Their confessions provided long-awaited answers in a mystery that gripped Philadelphia and much of the region for days.

According to CNN, DiNardo's history of mental illness includes involuntary commitment, a schizophrenia diagnosis and repeated contacts with police. He also suffered a head injury last year in an ATV accident.

The commitment meant he was barred from possessing guns, but nonetheless, he had one in February when police charged him with having a shotgun. The original charge was dismissed by a judge in May, and the Bucks County district attorney's office authorized police to reinstate and refile that charge on June 21.

He was not arrested again on the charge until July 10, days after the men went missing. He also used at least two guns in the slayings of the four men, investigators said. He was arrested again on Wednesday for allegedly stealing and attempting to sell Meo's vehicle the day after Meo was reported missing.

Dinardo's bail was set at $5 million after the district attorney argued that he was a flight risk.

Kratz, too, has several criminal arrests. Most recently, he was charged in February with burglary, conspiracy, criminal trespassing, theft, receiving stolen property and criminal mischief. He was out on bail at the time of the killings.

At a news conference in Doylestown, Weintraub confirmed that the bodies discovered in the common grave had been identified as those of Dean A. Finocchiaro, 19, of Middletown Township; Thomas C. Meo, 21, of Plumstead Township; and Mark P. Sturgis, 22, of Pennsburg, Montgomery County.DiNardo himself led investigators to the fourth victim — Jimi T. Patrick, 19, of Newtown Township — and it was then that DiNardo implicated his cousin in the slayings of the other three only after prosecutors agreed they would not seek the death penalty against him. All four appeared to be tied to DiNardo through school or social interactions, based on accounts from friends and a review of their social media accounts.

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," Weintraub said at a news conference, explaining the surprise plea agreement forged Thursday that led them to the final body. "There was an attempt to burn the bodies, to deface them, to obliterate them, but I don't believe that that was successful," Weintraub said.

Jimi Patrick's family and friends issued the following statement to ABC News on Friday: "We would like to thank everyone for your continued prayers and loving thoughts for both our family and for the other three families during this time of grief. Jimi was an amazing and genuine soul that left us too soon. He was the type of person capable of making anyone laugh whether it be from his sarcastic jokes or his contagious laugh. Aside from his humor, Jimi was incredibly loving and sweet when it came to those closest to him as well as anyone he crossed paths with. We plan to hold all the dear moments we have with him close to our hearts while we seek justice for his untimely passing."

Both men are charged with homicide, conspiracy, abuse of corpses and other crimes. DiNardo faces a mandatory sentence of life in prison if convicted. Weintraub hasn’t said if he will seek the death penalty for Kratz.

As he was led from the Bucks County courthouse complex in handcuffs and leg shackles after his confession, DiNardo muttered only two words in response to reporters’ shouted questions:

“I’m sorry.”