DOYLESTOWN -- The mystery that has transfixed the Philadelphia area over the past week -- the disappearance of four young men -- took a grisly turn when human remains were discovered in a 121/2-foot-deep grave on a farm. But exactly what sort of evil befell them, and why, remained shrouded in secrecy.

The prosecutor who has held twice-daily briefings made it clear Thursday he knows a lot more than he is saying, citing the need to protect the investigation. That has only added to the speculation and rumors.

"It's been very unnerving. It's very spooky," said Laura Hefty, who lives a few miles from the gravesite in Solebury Township, where farms bump up against new residential developments.

Many people, she said, are trying to convince themselves this is nothing that could ever happen to their kids.

"Some people are pretty angry, too," and are asking, "How did it get this bad?" she said.

The four men, all residents of Bucks County, disappeared last week. At least three knew each other. The remains of only one, 19-year-old Dean Finocchiaro, have been identified, though authorities said other remains were found in the hole as well.

Cosmo DiNardo, the 20-year-old son of the farm property's owners, has been named by police as a person of interest in the investigation. He is being held on $5 million cash bail, accused of trying to sell one of the victims' cars.

District Attorney Matthew Weintraub said he was weighing more serious charges but stopped short of calling DiNardo a suspect. He parried one question after another by saying he couldn't -- or wouldn't -- answer.

Police were back at the farm Thursday, digging away in the dust and the 90-degree-plus heat and using plywood to shore up the deep, tent-covered trench that they excavated at the spot where Weintraub said dogs managed to "smell these poor boys 121/2 feet below the ground."

For days, TV news helicopters have trained their cameras on the excavation, creating an unsettling racket but allowing the public to follow the forensic work from their office computers. On one day, viewers could watch investigators haul up buckets of dirt and sift it through hand-held screens in what looked like an archaeological dig.

"They're tenderly, painstakingly, reverentially recovering the remains of people they do not even know," Weintraub said.

When the prosecutor held a dramatic midnight Wednesday news conference to announce the discovery of remains, Claire Vandenberg, 18, 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."

"It seemed almost like a horror film or something, just unraveling before our eyes," she said.

Authorities have not revealed any details about how the victims found in the grave may have died or how they got there. The prosecutor had said at one point that he thought a backhoe may have been on the property.

"This is a homicide. Make no mistake about it. We just don't know how many homicides," Weintraub said at his middle-of-the-night news conference.

Susan Coleman told news outlets that she and her husband were in their backyard last Saturday afternoon when they heard several rounds of what they believed was shotgun fire coming from the direction of the DiNardo farm.

"This person was going bananas," she told phillyvoice.com.

Eric Beitz, who said he had hung out with Cosmo DiNardo in recent weeks, told philly.com that DiNardo routinely sold guns and on multiple occasions had talked "about weird things like killing people and having people killed."

DiNardo, whose parents own construction and concrete businesses in the Philadelphia area, has had a few brushes with the law over the past year.

He was arrested on Monday on an unrelated gun charge dating from February, accused of illegally possessing a shotgun and ammunition after being involuntarily committed to a mental institution.

His father bailed him out, but he was jailed again later in the week on the stolen-car charges, and bail was set much higher, after a prosecutor said he was a danger to the community because he had been diagnosed as schizophrenic.

His 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.

His attorney, Fortunato Perri Jr., wouldn't comment Thursday.

The other missing men are Mark Sturgis, 22, and Thomas Meo, 21, who worked together in construction, and Jimi Taro Patrick, 19, a student at Loyola University in Baltimore. Patrick and DiNardo had attended the same Catholic high school for boys.

It was the discovery of Meo's car on a DiNardo family property a half-mile from the farm that led to Cosmo DiNardo's re-arrest.

An attorney for DiNardo's parents said they sympathize with the families of the missing and are cooperating in the investigation.