DiNardo, 20, is ready to plead guilty to four counts of first-degree murder, attorney Paul Lang said.
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"I'm sorry," DiNardo is heard to say as police led him away from a building near the Doylestown courthouse on Thursday evening.
TIMELINE: Disappearance of 4 men in Pennsylvania
DiNardo has told investigators where all of the bodies are, according to Lang.
"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," Lang said. "He was very forthright and gave all relevant details that he could."
Lang was asked if the nature of his confession meant others might be involved in the crimes, but he refused to comment. He said he would leave specifics for law enforcement.
There has been no immediate comment from the district attorney's office. A news conference is expected at some point Thursday night.
DiNardo has "deep remorse" for what he did, Lang said.
RELATED: Human remains discovered in Pennsylvania; one missing man identified
Human remains have been found amid an extensive search on farmland owned by DiNardo's family in Solebury Township. A body found there has been identified as that of 19-year-old Dean Finocchiaro.
Finocchiaro, 22-year-old Mark Sturgis, 21-year-old Tom Meo and 19-year-old Jimi Patrick have been missing since last week.
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Authorities were not yet ready to identify any other remains, Weintraub said at a news conference on Thursday morning.
Weintraub says they found the remains in a 12.5-foot-deep common grave on the sprawling farm. Crews have been working around the clock to search the property.
Patrick was a year behind DiNardo at a Catholic high school for boys, the Associated Press reports. It's unclear how well the four knew DiNardo, if at all.
DiNardo was arrested on Wednesday for the second time this week. The new charges allege that he tried to sell a car belonging to Meo a day after Meo was last seen.
According to investigators, Meo's girlfriend told investigators she last heard from him through a text message on July 7. On July 8, Meo's family reported him missing to authorities.
RELATED: Person of interest named in disappearance of 4 men
On July 9, Weintraub said, DiNardo allegedly tried to sell Meo's Nissan to a friend for $500. Weintraub said investigators know who that friend is, but they are withholding his identity "for potential safety."
The vehicle was later found at a property belonging to DiNardo's family on Aquetong Road in Solebury Township.
The title for the vehicle was unsigned, Weintraub said, indicating there was no legal exchange of ownership.
Investigators also allegedly found a diabetic kit inside the car. Meo is diabetic, Weintraub said, and is known to carry that "life-saving" kit with him.
Like Meo, Sturgis and Finocchiaro were last seen on July 7. Patrick was last seen on July 5.
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DiNardo is being held on $5 million full cash bail. The judge said it was the highest bail she has ever set.
A grand jury reportedly met at the Bucks County Courthouse in Doylestown. The parents of Cosmo DiNardo were subpoenaed to appear, sources tell Action News.
Attorney Fortunato Perri Jr. is representing Cosmo DiNardo. On Wednesday, he released a statement on behalf of his parents that reads:
"As parents, Mr. and Mrs. DiNardo sympathize with the parents and families of the missing young men and they are cooperating in every way possible with the investigation being conducted by law enforcement."
The DiNardo's own a concrete company in Bensalem.
DiNardo was arrested on Monday on charges from a weaopns incident in February. According to an affidavit of probable cause from that time, DiNardo was accused of possessing a shotgun and ammunition despite a history of mental illness that includes an involuntary commitment.
He was released on Tuesday on 10 percent of $1 million bail.
Sources tell ABC News that a ping from one of the missing men's cellphones led investigators to the farmland.
Investigators continue to ask the public for tips.
Anyone with information is asked to contact FBI investigators at 1-800-CALL-FBI, or go to tips.fbi.gov.