Two cousins were formally charged with murder in the killing of four young Pennsylvania men after confessing to a series of gruesome assaults with a rifle, handgun and backhoe following aborted marijuana deals.

Cosmo DiNardo, 20, and his cousin, Sean Kratz, 20, were also charged with conspiracy, robbery, abuse of a corpse and possession of an instrument of a crime.

DiNardo was the first to be arrested Thursday and confessed after authorities agreed not to seek the death penalty. He then led authorities to the site of the initial killing.

As police led the handcuffed suspect to a van Thursday evening, DiNardo said "I'm sorry" when asked by reporters whether he had sympathy for the victims’ families.

By the time of DiNardo's arrest, investigators had already found the bodies of Dean Finocchiaro, 19, Thomas Meo, 21, and Mark Sturgis, 22, in a 12-foot common grave on a 70-acre farm owned by the suspect's parents in Solebury Township, about 30 miles north of Philadelphia.

The criminal complaint said DiNardo told authorities the killings began July 5 after he agreed to sell Jimi Patrick, 19, the first victim, four pounds of marijuana for $8,000.

After driving to the farm to complete the sale, Patrick, a fellow student with DiNardo at a Catholic high school for boys, said he only had $800.

DiNardo then told Patrick he could sell him a shotgun instead and took him to a remote part of the property to give him the weapon. He said he then shot Patrick with a .22-caliber rifle and used a backhoe to dig a shallow grave to bury the body.

Finocchiaro was killed two days later after DiNardo agreed to sell him a quarter pound of pot for about $700. Before making the sale, DiNardo picked up his cousin, Kratz, and the pair decided instead to rob Finocchiaro.

The three men drove to the DiNardo farm and ended up in a barn where, according to the affidavit, Kratz shot Finocchiaro in the head with a handgun belonging to DiNardo's mother. DiNardo told authorities he then grabbed the weapon and shot Finocchiaro a second time. The two men stuffed the body into a metal tank known as a "pig roaster."

The last two victims, Meo and Sturgis, were killed the same evening as they got out of DiNardo's truck at the farm to buy pot.

"When they turn their backs on me, I shot Tom in the back," DiNardo told authorities, according to the complaint. Sturgis was shot as he tried to run away and fell to the ground.

DiNardo, who had run out of ammunition, then used the backhoe to run over Meo and haul all three bodies to one spot where they were buried in a common grave after he tried to burn the remains.

In a separate statement, Kratz largely corroborated DiNardo's story, saying Meo died after DiNardo "basically crushes him" with the backhoe.

Bucks County District Attorney Matthew Weintraub told reporters Friday that DiNardo's confession led investigators to uncover Patrick's body about a half mile away from the common grave "on top of a mountain."

Asked whether DiNardo's information was critical to finding the body, the district attorney told reporters: "We'd still be looking, I know that much."

Asked why he thought DiNardo decided to confess, Weintraub said, "I don't know what convinced him, I'd like to think he wanted us to get these boys home."

Eric Beitz, 20, of Bensalem, Pa., told The Philadelphia Inquirer that in recent weeks he and his friends hung out with DiNardo, who frequently sold firearms, spoke about killing people and seemed to have “ulterior motives.”

“I can tell you on multiple different occasions, on multiple different accounts, from multiple different people, including myself – Cosmo has spoken about weird things like killing people and having people killed,” Beitz said. “Everybody you talk to about this guy, you hear he’s mentally unstable.”

Earlier this year, authorities charged DiNardo with possessing a firearm despite an involuntary mental health commitment. In seeking $5 million bail on a stolen car charge related to the missing men this week, prosecutors said DiNardo had been diagnosed with schizophrenia. He also suffered a head injury after an ATV accident about a year ago.

Tina Finocchiaro, the victim's aunt, wrote on Facebook on Thursday morning: “I don’t have many words today I am completely crushed heartbroken and numb I lost my nephew to a crime that is unspeakable nobody should have to go through this my heart goes out to his parents and all of the other parents and I also want to thank reached out to us and prayed for for us.”