Video Shows Gilgo Beach Suspect's Arrest in Manhattan — and D.A. Explains Why He Was Detained There

Rex Heuermann, the suspect in the infamous Long Island Serial Killer case, was arrested Thursday on the sidewalk outside his Midtown, Manhattan office — and video footage first obtained by ABC 7 New York shows him being stopped by plainclothes officers in broad daylight as pedestrians walk by.

Suffolk County District Attorney Ray Tierney tells PEOPLE why authorities decided to take him into custody in Manhattan as opposed to closer to his Massapequa Park home on Long Island.

“He has 92 gun permits,” Tierney says. “We thought it would be safer to get him out of the house."

The prosecutor adds that Heuermann, 59, was arrested when he least expected it.

“I think he was pretty shocked,” Tierney tells PEOPLE. “He had no clue, which tells us that we did our job.”

Heuermann is accused of killing at least three sex workers more than a decade ago. The married father of two was charged Friday with three counts of first-degree murder and three counts of second-degree murder in the deaths of Melissa Barthelemy, 24, Megan Waterman, 22, and Amber Costello, 27.

He is also considered a prime suspect in the death of Maureen Brainard-Barnes, 25.

All four women had worked as online sex workers and had been missing between 2007 and 2010. Their bodies were found along a half-mile stretch of Ocean Parkway in Long Island, New York, in December 2010.

Investigators have since uncovered the remains of at least 10 people along Gilgo Beach, though they have said not all of them are believed to be connected to the same killer. The bodies have ranged in age from a toddler to adult and have included both men and women.

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Tierney previously told PEOPLE that Heuermann was allegedly linked to the killings using cell tower data, a witness’s description of his Chevrolet Avalanche, and eventually, from DNA from five hairs found on three of the victims.

Authorities have alleged that Heuermann committed the murders while his wife and two kids, who all lived with him at his Massapequa Park, N.Y., home, were out of state.

Tierney previously told PEOPLE that investigators are still looking into where the murders were committed.

According to the district attorney, Heuermann is expected back in court in early August. He has pleaded not guilty.