Investigators searching a sprawling suburban Philadelphia farm in the disappearance of four young men who vanished last week discovered human remains, including the body of one of the men, the authorities announced early Thursday morning.

The announcement came hours after the authorities charged the son of the farm’s owners, Cosmo DiNardo, with stealing one of the men’s cars and trying to sell it for $500. Mr. DiNardo, 20, came under scrutiny early in the investigation and has been identified as a “person of interest” in their disappearance.

The remains were discovered in a 12.5-foot-deep “common grave” on the Bucks County farm, where local authorities, as well as an evidence response team from the Philadelphia office of the F.B.I., have brought in cadaver dogs, sifted through soil in rows of corn stalks, dug up concrete with a backhoe and surveyed the land on all-terrain vehicles.

Cadaver dogs led detectives to the grave, the Bucks County district attorney, Matthew D. Weintraub, said at a news conference early Thursday morning. He said the authorities recovered the body of Dean Finocchiaro, 19, who vanished around 6:30 p.m. Friday in Middletown Township.

Mr. Weintraub said other human remains were also discovered, but he did not say whether they belonged to the three other men.

The developments on Wednesday signified a major shift in the investigation of the disappearance of the four men over two days last week. The authorities in Bucks County, a fast-growing suburb with rolling hills and vast estates, have called the painstaking search among the largest law enforcement efforts in the county’s history.

The police arrested Mr. DiNardo on Wednesday afternoon, a day after his father paid 10 percent of a $1 million bond to bail him out of the Bucks County Jail on an unrelated felony weapons charge. Mr. Weintraub described Mr. DiNardo as a flight risk, and a judge on Wednesday afternoon set his bail for the new charges, both felonies, at $5 million.

Mr. Weintraub said early Thursday that detectives were going to “seriously look” at pursuing homicide charges. “We bought ourselves a little bit of time with charging Mr. DiNardo with the stolen car,” he said.

Since Saturday afternoon, they have centered their search on the farm belonging to Mr. DiNardo’s family in Solebury Township, about 30 miles north of Philadelphia.

Aerial photos of the farm on Wednesday showed that the authorities were focusing on a patch of land off a dirt road behind a home, where they erected several large tents and used tarps to collect dirt. Concrete blocks were stacked in a pile nearby.

As the search entered its fifth day on Wednesday, Mr. Weintraub again expressed confidence that the authorities were searching in the right area. The police have cast a wide net, but have devoted the bulk of their resources to the family’s farm because of several clues.

“We are going to find something for sure, I have no doubt of that,” Mr. Weintraub said at a news conference on Wednesday afternoon near the DiNardo farm. “I cannot really confirm more, but we’ve been utilizing resources that I didn’t even know existed. I’m very encouraged by that, at the least, that we are going to find some finality in this prolonged ordeal.”

On Saturday, the police tracked a signal from the cellphone belonging to Mr. Finocchiaro to the farm. Early Sunday morning, a 1996 Nissan Maxima belonging to another missing man, Tom Meo, 21, was found less than a mile from the farm, at another property owned by the DiNardo family, according to court records. A Nissan sedan owned by Mark Sturgis, 22, was also found Sunday morning, at an outdoor shopping center down the road from the farm. The fourth missing man, Jimi Tar Patrick, 19, was last seen on Wednesday.

The police started to closely examine Mr. DiNardo’s possible role in their disappearance early on in the search, and Mr. Weintraub first identified him on Tuesday as a “person of interest” in the case. His home in Bensalem Township, about 30 miles from the farm, was searched on Monday, the same day he was arrested on a previously dismissed weapons charge.

The farm in Solebury Township is owned by his parents, Anthony and Sandra DiNardo. Responding to reports that the parents were summoned to a grand jury hearing, Mr. Weintraub declined to discuss whether one was hearing the case.

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In addition to the cars’ locations at or near the DiNardo family’s properties, the police said, officers have also uncovered other clues, which came to light in court records on Wednesday.

Shortly before 8 p.m. last Friday, a license plate reader on a Solebury Township police car captured the license plate of a silver Ford truck, which Mr. DiNardo later told the police he was driving that night. Two seconds later, the license plate reader registered Mr. Meo’s Nissan Maxima driving by. That location is about two miles from where Mr. Meo’s car was discovered on Sunday.

Later on Sunday, a friend of Mr. DiNardo’s told the police that he tried to sell him an older model Nissan Maxima, according to court records. An unsigned title for Mr. Meo’s Maxima was found next to the car. “There was no legal exchange of that vehicle,” Mr. Weintraub said.

A diabetic kit belonging to Mr. Meo, who has diabetes, was also found in the car. His parents told the police that their son never traveled without it. Asked if Mr. Meo could survive without it, Mr. Weintraub said on Wednesday, “It is my understanding that he could not, that he would go into diabetic shock.”

The arrest of Mr. DiNardo on Monday stemmed from a February episode in which the police in Bensalem Township found him with a 20-gauge shotgun, according to court records. He was not legally allowed to possess it because he had been involuntarily committed to a mental institution.

A judge dismissed that charge in May. But the Bucks County district attorney’s office wanted to pursue the case again and asked the Bensalem police in a June 21 letter to rearrest Mr. DiNardo. They did not arrest him again until on Monday, after detectives were searching his family’s farm.