Investigators who found the body of one of four missing friends in a common grave filled with human remains north of Philadelphia have charged a fifth young man with trying to illegally sell one of the youth's cars. The 90-acre farm where the remains and the stolen vehicle were found is owned by the suspect's parents.

The FBI has spent several days digging up the grave and sifting through the dirt for evidence.

“This is a homicide; make no mistake about it. We just don’t know how many homicides,” Bucks County District Attorney Matt Weintraub said at a midnight news conference Thursday.

Authorities said they are looking at pursuing homicide charges against 20-year-old Cosmo DiNardo, who was hit by a $5 million cash bail on Wednesday in the stolen car case, two days after he was released on $1 million bail on an unrelated gun charge.

The earlier charge stems from accusations that DiNardo was caught with a shotgun and ammunition in February despite a prior mental health commitment. An affidavit in that case said he is “known to be suffering from mental illness.”

The body found in the 12 1/2 foot common grave on Wednesday was identified as Dean Finocchiaro, 19. Also missing are 22-year-old Mark Sturgis, 21-year-old Tom Meo and 19-year-old Jimi Tar Patrick. Patrick, who attended a Catholic high school for boys with the DiNardo, was last seen Wednesday, while the other three vanished Friday.

Meo's grandfather, Chuck Meo, told an NBC News producer that crews found the remains under a blue tarp after lifting out a propane tank, WCAU-TV reported.

DiNardo was charged after authorities, using license tag tracking devices, found Meo's 1996 Nissan Maxima on the same farm where the body was discovered.

Weintraub said investigators found Meo's critical diabetes treatment kit in the car. The criminal complaint in the case said the keys and title to the car were found hanging up on the wall inside the garage of the property. Authorities said the title had not been signed, indicating that Meo had not transferred title to anyone or authorized its sale.

Weintraub said an unnamed witness told authorities that DiNardo had attempted to sell the car to him for $500.

At least some of the missing men are friends, but it’s unclear how well they knew DiNardo, if at all.

Eric Beitz, 20, of Bensalem, said Wednesday that he and his friends had spent time recently with DiNardo, who 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 told The Philadelphia Inquirer. “Everybody you talk to about this guy, you hear he’s mentally unstable.”

According to Beitz, DiNardo also sold marijuana and guns, and aggressively sought new customers. Teens regularly circulated DiNardo’s number, he told the newspaper.

DiNardo’s parents, Antonio and Sandra DiNardo, own the farm in upper Bucks County, a bucolic area with rolling hillsides, new housing developments and historic sites. They also own a nearby farm parcel that was also searched and a concrete company near their home in Bensalem, closer to Philadelphia.

An attorney representing the couple issued a statement earlier Wednesday saying they sympathize with the families of the missing men and are cooperating “in every way possible with the investigation.”

DiNardo's social media posts suggest an avid interest in hunting, fishing and Air Jordan sneakers, which he appeared to sell online. He had enrolled in a nearby college at one point as a commuter student, with hopes of studying abroad in Italy, according to an article on the college website. He had a few other brushes with the law since turning 18 over traffic violations and other minor infractions.

Contributing: Associated Press