The search for four missing young men entered its fourth day Wednesday in Bucks County, Pennsylvania. As investigators and volunteers scoured a 90-acre property for any sign of the men, authorities said the breadth of the case was beyond imagination.

“I am still encouraged by the pace of the investigation, but as you can imagine, it’s just massive in scope,” Bucks County District Attorney Matthew Weintraub said in a press conference Tuesday. “Take the biggest [investigation] you’ve ever seen and multiply it by a million.”

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Jimi Patrick, 19, Tom Meo, 21, Mark Sturgis, 22, and Dean Finocchiaro, whose age was either 18 or 19, were all seen for the last time last week. Authorities said they thought the men knew each other, though they were working to confirm how.

Armed with shovels and construction equipment, 40 to 50 people searched the 90-acre property in Solebury Township, about 30 miles north of Philadelphia. The residence belonged to the parents of Cosmo DiNardo, who was arrested Monday as a person of interest in the case.

DiNardo, 20, was arrested on unrelated firearm possession charges and authorities were quick to caution that he was not a suspect in the case. A ping from one of the men’s cellphones led investigators to search the property, a source told WPVI. Authorities also received tips saying DiNardo was seen with the men before they went missing.

“We are gradually sifting through the property,” said Weintraub. ”Its 90-something acres and we are going through it with the equivalent of a fine-toothed comb. It’s going to take us a very long time to get through it.”

A piece of forensic evidence uncovered was of interest to the investigators, though no additional details were given, according to WCAU.

“The leads are incredibly hot,” Weintraub said at a press conference Monday. “They’re fruitful. We’re making great progress. But there’s so much more work to do.”

Weintraub said he believed foul play was involved in the disappearances.

“We’ve been treating this from the outset as a criminal investigation,” he said. “And nothing has deterred from this point.”

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Five local law enforcement agencies, Pennsylvania state police, the FBI and United States Marshals were all involved in the investigation. Weintraub said it was unclear whether the men were alive at this point.

“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.”