Action News reporters Walter Perez and Katherine Scott were there as search crews arrived.
What appeared to be a bus full of law enforcement cadets just pulled in to the search-site in Solebury. Search-team? pic.twitter.com/9fVPoAQhoe— Walter Perez (@WalterPerez6abc) July 11, 2017
Search crews showing up to site on Lower York Rd to continue looking for four young men. pic.twitter.com/BX1HkQqdH3— Katherine Scott (@KScott6abc) July 11, 2017
Cosmo DiNardo, 20, was taken into custody on Monday and charged with a firearms possession offense from February.
According to an affidavit of probable cause obtained by Action News, DiNardo was accused of possessing a shotgun and ammunition despite a history of mental illness that includes an involuntary commitment.
The charge had been dropped, but was refiled Monday.
It was not yet known if DiNardo is suspected of having any involvement in the disappearance of the four men.
He is being held on $1 million bail.
Authorities released the booking photo of DiNardo on Monday night.
DiNardo was taken into custody at a home in the unit block of Wayland Circle in Bensalem. It was one of the multiple locations being searched by authorities on Monday.
His family owns that home, along with the property on Aquetong Road that was searched on Sunday, and a farm on Upper Mountain Road near Route 202 in Solebury Township that was the scene of an active search on Monday.
Bucks County District Attorney Matt Weintraub said he believes foul play is involved.
"I sure believe there is," he said during a news conference on Monday afternoon.
The FBI has joined the investigation. Weintraub said the leads in this case are "very hot."
"We've been treating this from the outset as a criminal investigation, and nothing has deterred that to this point," Weintraub said.
But when asked why he believes foul play was involved, he said it was due to "information that I know that I can't share."
Chopper 6 was over the farm in Solebury Township, where a number of police vehicles and a mobile command center could be seen.
"We're not exactly sure what we're going to find there, but we're pretty confident that the investigation is proceeding in the direction we believed that it would," Weintraub said.
VIDEO: Chopper 6 over search scene in Solebury Twp.
The missing men are identified as Mark Sturgis, 22, of Pennsburg; Tom Meo, 21, of Plumstead; Dean Finocchiaro, 19, of Middletown Twp.; and Jimi Tar Patrick, 19, of Newtown.
Sturgis, Meo and Finocchiaro were last seen on Friday. Patrick was last seen on Wednesday.
Earlier Monday, the parents of Mark Sturgis confirmed his car was found at Peddler's Village in Bucks County. Sturgis' father also said his son was last seen with Meo.
The wooded area being searched is also near Peddler's Village.
Meanwhile, a car belonging to Meo was found on the property on Aquetong Road.
Weintraub said it is believed all four men know each other, but investigators are working to confirm that information.
At this point, Weintraub said it is "all hands on deck" to find the four men. He could not confirm if all four are still alive.
"I can't say. We hope they are, but we need to go where the investigation leads us," Weintraub said.
For now, he is asking for the community's prayers.
"At this point I ask for your patience and your prayers for these four young men and let us do our jobs," Weintraub said.
Anyone with information is asked to contact investigators at 215-297-8201.