(NEXSTAR) – “Backdraft” actor Billy Baldwin said Friday that he and Rex Heuermann, the suspect accused in a string of murders on Long Island, attended the same school in the late ‘70s-early ‘80s.

“Woke up this morning to learn that the Gilgo Beach serial killer suspect was my high school classmate Rex Heuermann,” Baldwin tweeted, calling the discovery “mind-boggling.”

Baldwin, whose famous family includes actors Alec Baldwin and Steven Baldwin, was born in Massapequa, New York — the same Long Island town where Heuermann said he’d lived all his life, Nexstar’s WPIX reported.

Baldwin also identified Massapequa’s Berner High School as his and Heuermann’s alma mater — a claim many of the school’s alumni have seemingly confirmed on Facebook since Heuermann’s arrest.

Heuermann, a 59-year-old architect, was arrested Thursday night near his Fifth Avenue office, police said. He has been charged with first-degree murder in the deaths of Melissa Barthelemy, Megan Waterman and Amber Lynn Costello — three of nearly a dozen victims in a long-unsolved string of killings known as the Gilgo Beach murders.

He is also considered the prime suspect in the death of a fourth woman whose body was bound and hidden in thick underbrush along a remote beach highway, authorities said.

Investigators say they linked hairs found on the victims to Heuermann’s wife, according to court documents. They also linked a male hair found on Waterman to a hair they found in a pizza box he had thrown away near his Manhattan office.

Officials say additional evidence linking Heuermann to the killings included phone records and internet search activity.

Heuermann’s lawyer said his client has maintained his innocence, saying he “didn’t do this.”

Baldwin, in his tweet on Friday, did not detail any familiarity with Heuermann other than confirming they attended the same school. He did suggest, however, that Massapequa “is in shock” over the news.

Baldwin, 60, has appeared in dozens of films since the late ‘80s, including “Flatliners,” “Fair Game,” “The Squid and the Whale” and “Forgetting Sarah Marshall.”

The Associated Press contributed to this report.