Police in Bucks County, Pennsylvania, say it's an "all-hands-on-deck situation" because four young men are missing.
Police have been searching cornfields and shutting down roads looking for the men.
The men are between 18 and 22 years old, and police say all disappeared within days of each other.
Two of them are best friends who work together in construction. Another is a mutual friend.
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Investigators do believe foul play is involved.
Sources told NBC Philadelphia Monday evening a man in custody on unrelated charges could be connected to the disappearance of the four men. That same source says Cosmo Dinardo is not considered a suspect.
"Missing is missing, whether you don't want to be found or you've been reported missing by somebody that fears the worst," said Matt Weintraub, the district attorney for Bucks County. "We're going to be treating this like they're missing and we need to try to find them to make sure they're safe if we can."
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Police are focusing the search on one piece of property.
In a news conference late Monday, Weintraub said there is a huge investigative team working the area right now.
More information is expected to be released on Tuesday.