Actor Billy Baldwin revealed that he once knew Rex Heuermann, the Long Island, New York man arrested in connection to the murders of multiple young women found buried on Gilgo Beach.

Heuermann was arrested in Manhattan on Thursday evening, Suffolk County Police Commissioner Rodney Harrison announced in a press conference Friday. He has been charged with first- and second-degree murder in the deaths of Melissa Barthelemy, Megan Waterman and Amber Costello. Authorities described his as a “prime suspect” in another killing, according to the Associated Press.

He appeared in court Friday afternoon, where he pleaded not guilty to all the charges against him.

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Baldwin, whose brother is Alec Baldwin, reacted to reports of Heuermann’s arrest on Twitter, writing, “Woke up this morning to learn that the Gilgo Beach serial killer suspect was my high school classmate Rex Heuermann.”

According to Baldwin, he and Heuermann were both in the graduating class of 1981 at Berner High School in Massapequa, New York. 

“Married, two kids, architect. ‘Average guy… quiet, family man.’ Mind-boggling… Massapequa is in shock. 23andMe strikes again???,” he wrote, referencing the recent uptick in arrests thanks to genetic genealogy technology.

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However, it appears that Heuermann wasn’t linked to the crimes by the genealogy site, according to a bail application obtained by NBC News. The application states that he registered a first-generation Chevrolet Avalanche, which an eyewitness reported seeing the night 27-year-old Amber Lynn Costello disappeared on September 2, 2010. Using that tip, law enforcement began investigating Heuermann’s whereabouts on the nights that the victims went missing through cell phone records.

Investigators later tied him to the crimes through DNA found in one of the graves using a box of pizza he discarded, according to NBC News.

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As investigators reportedly searched Heuermann’s home on the south shore of Long Island, reporters spoke to his neighbors, including 64-year-old Patricia Maressa, who described him to NBC News as a “tall, big, big guy. Always well dressed.”

“I’m still shocked that this is going on,” she said. “It’s a very quiet neighborhood. At night, you could hear a pin drop.”

Heuermann owned his own architecture firm, RH Consultants and Associates, with an office in Manhattan. According to his firm’s website, his client list includes Catholic charities, American Airlines, Target, Foot Locker, and Nike, among others. His website’s “about” section also states that he “provided services to other city agencies, not-for-profit agencies, builders, developers, and individual owners of buildings.”