Matthew Branning and Michael Stark had known each other for only about a month, investigators said Wednesday. So when both men disappeared after leaving their workplace in Bucks County — as if they “ceased to exist,” as District Attorney Matt Weintraub put it — authorities began to suspect that something was wrong.

“It’s not my experience that two people that have no other attachment go missing on the same date at the same time,” Weintraub said at a news conference. “I don’t believe in coincidences, frankly, and I do suspect foul play.”

Stark, 47, of Royersford, is now considered a person of interest in the disappearance of Branning, 50, of Sellersville, police said. The men both worked at Enchlor Inc., a company in Silverdale that manufactures and assembles water-treatment systems for countries outside the U.S.

Both were seen working there on Oct. 15, Weintraub said. Later that night, a security camera at a local BB&T Bank branch recorded Branning withdrawing $500 from an ATM, with another person visible in the back seat. Cell-phone data from Branning’s phone, as well as toll information, showed his 2002 Lexus sedan traveling into New Jersey, and later Cape May, according to Weintraub. That was the last trace of Branning that investigators found.

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Stark, for his part, was recorded making a purchase at a Wawa in Cape May, before traveling north and then west on the Atlantic City Expressway. Branning was not seen with him, Weintraub said. Stark wasn’t seen again until Nov. 13, when he was spotted at a pawn shop in Michigan trying to sell a bicycle.

Branning’s disappearance, and the lack of information about Stark’s whereabouts, have left Branning’s family bitterly frustrated. His younger brother, Timothy, said the situation has been especially difficult for their 84-year-old mother, who was hospitalized for several days the week after he went missing.

“It’s difficult, because it’s still an open wound with no closure, and the investigation has been dragging out,” Timothy Branning said in an interview Thursday.

Branning said Stark took advantage of his brother’s kind nature, often asking him for rides to and from work, a 45-minute trip. He fears that Stark preyed on that kindness.

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“My brother was a decent guy, no criminal record, no history of violence,” Branning said. “He absolutely would’ve given him money, if [Stark] gave him enough of a sob story.”

Weintraub noted that there is a bench warrant out for Stark’s arrest in Monroe County — about two hours north of Philadelphia — for failing to show up in court on charges of resisting arrest and drug possession and he will be extradited if taken into custody anywhere else. The district attorney asked anyone with information to come forward.

“We are making a plea for your help,” Weintraub said. “We don’t want the case to go cold, and let us be the judge of whether your information is helpful or not.”

Anyone with information about the case is asked to call Bucks County detectives at 215-945-3100.