In the space of two days, four college-aged men vanished. Then a mass grave was found.

A 20-year-old man has confessed to being involved in the murders of four college-aged men who went missing within the space of two days of each other in eastern Pennsylvania, CNN reports.

Nineteen-year-old Jimi Patrick was reported missing on July 6 after he failed to show up for work, with friends and family concerned about his lack of contact since the evening before. Just two days later, 19-year-old Dean Finocchiaro, 22-year-old Mark Sturgis, and 21-year-old Thomas Meo also went missing, with close friends of Sturgis and Meo also raising alarm when they too failed to show up for work.

Just over a week after Patrick first went missing, 20-year-old Cosmo DiNardo – who attended the same Catholic high school as one of the men – admitted to involvement in their deaths and told authorities the location of their bodies, The Guardian reports his defence attorney said on Thursday.

The confession came after the body of Finocchiaro was found on the family farm where DiNardo lives with his parents. And as investigators began working to excavate a 3.6m deep grave where the body was found along with other human remains. The other remains are yet to be identified.

“He confessed to his participation or commission in the murders of four young men,” Paul Lang, one of Dinardo’s lawyers said, according to The Washington Post. “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 his client was ready to plead guilty to four counts of first-degree murder.

Dinardo became a person of interest in the case after he allegedly tried to sell Meo's 1996 Nissan Maxima the day after Meo was reported missing. According to District Attorney Matthew Weintraub, who spoke to reporters, Meo's life-saving diabetic kit was still in the vehicle.

"We are not done yet. This is a homicide, make no mistake about it," Weintraub told reporters. "We just don't know how many homicides."