(Amber Ferguson/The Washington Post)

Jimi Patrick was the first to go missing.

The 19-year-old vanished last week. Days later, three other young men — all between the ages of 19 and 22 — also disappeared, setting off an intensive, grueling search at a farm here in the rolling country north of Philadelphia.

The search took a series of grim turns Thursday, as authorities said cadaver dogs had led them to the body of one of the missing men at the bottom of a 12-foot grave. There, police found other human remains that have not been publicly identified. Hours later, a 20-year-old man whom police had considered a person of interest confessed to playing a role in the slaying of the four missing men, according to his attorney.

Prosecutors had vowed to bring answers to the families of those who had disappeared, a mystery that has gripped Bucks County.

“This painstaking process will go on,” Matthew D. Weintraub, the county’s district attorney, said at a briefing Thursday. “We’re going to bring each and every one of these lost boys home to their families one way or another. We will not rest until we do that.”

Investigators had focused their search on a property a few miles from the Delaware River, a farm owned by the parents of Cosmo Dinardo, the man who has been identified as a “person of interest” in the case. Dinardo was arrested Wednesday and accused of stealing and trying to sell a car belonging to one of the missing men, and he was being held in jail on $5 million cash bail after being deemed a flight risk.

On Thursday, Dinardo confessed to his role in the homicides, one of his attorneys said.

“He confessed to his participation or commission in the murders of four young men,” Paul Lang, one of Dinardo’s defense lawyers, told reporters. “In exchange for that confession, Mr. Dinardo was promised by the district attorney that he will spare his life by not invoking the death penalty.”

It is unclear whether others participated in the slayings, and a spokesman for the district attorney’s office declined to comment on Lang’s statements. Early Thursday evening, the extent and conditions of the apparent plea deal remained unknown, and Dinardo had not been charged in connection with the slayings.

Dinardo apologized to relatives of the victims on Thursday as he left the county courthouse. Reporters asked Dinardo, who was wearing an orange jumpsuit and had his hands shackled, what he would say to the relatives of the victims.

“I’m sorry,” Dinardo said before climbing into a police vehicle.

Dinardo has a history of unspecified mental illness, and he was previously involuntarily committed to a mental health institution after firing a shotgun, authorities said. No one answered when a Washington Post reporter visited an address listed for Dinardo in court filings, a large house with a swimming pool on a quiet cul-de-sac. A neighbor said Dinardo was one of four children.

Matthew Weintraub, District Attorney for Bucks County, Pa., speaks with members of the media in New Hope, Pa., on Thursday. (Matt Rourke/Associated Press)

Many questions still remained in the case, including precisely how Dinardo is connected to the four men — who, one by one, began to disappear last week — or why they might have been at the farm.

Authorities were making good progress among the farm’s dirt roads and knee-high corn Thursday, Weintraub said, though he declined to elaborate. Weintraub said law enforcement officers scouring the farm were enduring “incredibly stifling heat” as they searched, saying that the hole where the remains were found was 12 feet deep “and getting deeper.”

Not far from the property — owned by Dinardo’s parents, Antonio and Sandra, according to prosecutors — shops line Route 202 in one of the most historic and pastoral parts of America. “Fresh Eggs: 1000 feet” says one sign. “Organic Farm: Do not spray,” says another.

Bucks County District Attorney's Office photos show, from left in top row, Dean Finocchiaro, 18, and Tom Meo, 21. From left in bottom row: Jimi Patrick, 19, and Mark Sturgis, 22. (via Reuters/via Reuters)

Drone footage shows that the search teams have been working under a large tent, obscured by trees from the main road and the side roads. The farm is a few miles west of New Hope, a historic town that draws a heavy tourist crowd looking for antiques and vintage clothing. The two-lane road between New Hope and the county seat of Doylestown has numerous antique stories and a place called Peddler’s Village.

Traffic on the road is relatively heavy — because this rural place wants to be found by tourists. Locals say they’re not alarmed, even as they say things like this — a sprawling murder mystery — just don’t happen in that area.

James Jackman, a 19-year-old who works at Antiques at the Old Church, right next to the farm, said that for this part of Pennsylvania to have a homicide investigation is “definitely out of character.”

The case so far is shot through with questions of motive, method and timing. The Philadelphia Inquirer reported that a man who lives near the property said he had heard gunshots on Friday night and had given surveillance footage to police.

“It’s been crazy,” said a neighbor who lives near the farm, declining to be identified because of the nature of the case. “It’s all a mystery.”

Patrick was last seen July 5. His family released a statement Thursday describing him as a longtime baseball player — an excellent pitcher and hitter, they said — who recently finished his freshman year at Loyola University in Baltimore. The school hosted a prayer service for him Wednesday.

Early Thursday, Weintraub said authorities had identified the body of Dean Finocchiaro, 19, in the common grave. Thomas Meo, 21, and Mark Sturgis, 22, also remain missing. Weintraub said officials had classified the case as a homicide investigation, “we just don’t know how many homicides.” He did not say how Finocchiaro was killed.

Authorities said they have come up with more information about relationships between the men than they have made public, but details have begun to emerge in court filings, news reports and social media postings.

Meo and Sturgis — who are good friends and work together, according to court records — first met Dinardo when he was looking to sell marijuana to them, one of Meo’s friends told the Philadelphia Inquirer. Dinardo and Patrick both went to Holy Ghost Preparatory School in Bensalem, Pa., while Dinardo and Finocchiaro had both posted on a Facebook page for buying and selling all-terrain vehicles, the newspaper reported.

Meo’s girlfriend last heard from him in a text message on July 7, according to court records, and he did not show up for work on July 8. That same day, his mother reported him missing. Sturgis was last seen July 7, court records show. He also did not show up for work July 8 and was reported missing the next day.

This photo provided by the Bucks County District Attorney's Office in Doylestown, Pa., shows Cosmo Dinardo, who was arrested Monday. His lawyer says he confessed to taking part in the slayings of four men. (via Associated Press)

On July 9, cars belonging to Meo and Sturgis were found about two miles apart. That same day, Bucks County detectives interviewed a man from Bensalem, Pa., who said that Dinardo had offered to sell him an older model Nissan Maxima for $500.

Detectives wrote that they believe Dinardo had illegally taken Meo’s car, and they said Meo’s insulin kit — needed to treat his diabetes — was found inside. Meo could not survive without the insulin kit, Weintraub’s office said.

Dinardo was arrested Wednesday and charged with trying to sell Meo’s car, a 1996 Nissan Maxima with Pennsylvania plates. As of Thursday evening, he had not yet been charged in the slayings.

Earlier Thursday, Weintraub said Dinardo remained a person of interest, but the prosecutor emphasized that the investigation is “wide open.”

“We don’t pick a person and then try to build a case around that person,” Weintraub said at a news briefing. “That’s not fair to anyone. As of this moment, he remains a person of interest. But if others arise and we can name them, we will.”

Neighbors on the cul-de-sac where Dinardo lives described him as a good kid who went out of his way to help others — such as volunteering to shovel them out during snowstorms and refusing payment — noting that the slayings were shocking.

“Beautiful family,” said a neighbor, who spoke on the condition of anonymity. “I don’t know what went wrong with the kid. Great kid. Just saw him last week. Never a sign of problems.”

The FBI is assisting the Bucks County prosecutor’s office with the investigation, sending out an evidence response team and helping local detectives manage incoming tips, a bureau spokesman said.

Though Dinardo’s attorney said he confessed to avoid the death penalty, the practice is rarely used in Pennsylvania, with just three executions since 1976, among the fewest of any state with capital punishment during that period. In 2015, Gov. Tom Wolf (D) announced a death penalty moratorium that remains in place.

Berman reported from Washington. Alice Crites, Emma Ockerman and Abigail Hauslohner in Washington contributed to this report.