(NewsNation) — NYPD officials said a gunman armed with an assault-style rifle killed four people in a Manhattan high-rise building that houses the NFL headquarters and several financial firms before turning the gun on himself.

The gunman, Shane Tamura, 27, was believed to have acted alone in the shooting. An official motive has not yet been released.

Here are the victims of Monday evening's shooting and what we know about them so far.

Didarul Islam

Officer Didarul Islam, 36, was a veteran of the NYPD for more than three years. Authorities said he was off-duty and working as a private security detail when the shooting happened, according to NewsNation affiliate WPIX.

“He put himself in harm’s way. He paid the ultimate sacrifice," NYC Police Commissioner Jessica Tisch said. "Shot in col

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