Police said they suspected foul play after four young men went missing from Bucks County, Pennsylvania in a single week. Authorities continued their search Tuesday and said they were investigating “incredibly hot” leads.

“The leads are incredibly hot, they’re very fruitful,” Bucks County District Attorney Matthew Weintraub said Monday during a press conference. “We’re making great progress, but there’s so much more work to do.”

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Dean Finocchiaro, 18, and Jimi Tar Patrick, 19, were both reported missing last week, according to Bucks County Police. Mark Sturgis, 22, and Tom Meo, 21, were reported missing late Sunday. It remained unclear how the four were connected.

Authorities arrested a man Monday on unrelated charges though they called him a “person of interest” in the disappearance of the four men. Cosmo DiNardo, 20, was taken into custody Monday but police said he was not a suspect.

“Sometimes the chasm between a person of interest and being a person that is actually accused or arrested and certainly convicted of a crime is so wide that we never cross it,” said Weintraub.

The parents of one of the men, Mark Sturgis, confirmed that his car was found at Peddler’s Village in the County Monday, according to WVPI. They also said his son was last seen with another one of the men, Tom Meo and confirmed to the Associated Press that they were longtime friends who worked together in construction and that Finocchiaro was also a mutual friend.

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In addition to five local law enforcement agencies, the FBI and Pennsylvania state police also joined in the investigation.

“I don’t know how this is going to end up, unfortunately,” said Weintraub. “But I am confident that we are going to get to the bottom of this.”