The New York Police Department has identified the shooter of the city as Shane Tamura from Las Vegas who has ‘documented mental history.’

Tamura had killed four people at a NYC office tower on Monday, including an off-duty New York City police officer, Didarul Islam, and wounded a fifth before taking his own life.

“We are working to understand why he targeted this particular location,” police Commissioner Jessica Tisch said at a news conference.

Surveillance video shows a man exiting a double-parked BMW and carrying an M4 rifle before he walks toward the building. Tisch said he immediately opened fire on the New York Police Department officer as he entered the building and shot a woman who tried to take cover and then began “spraying” the lobby with gunfire, AP reported.

The man then made his way to the elevator bank and shot a security guard who was taking cover behind a security desk and shot another man in the lobby, the commissioner said.

The man took the elevator to the 33rd floor to a real estate management company and shot and killed one person on the floor. The man then walked down a hallway and shot himself, the commissioner said.

Officers found a rifle case, a revolver, magazines and ammunition in his car, Tisch said.

She said an initial investigation shows his vehicle traveled across the country through Colorado on July 26, then Nebraska and Iowa on July 27 and arrived in Columbia, New Jersey, as recently as 4:24 p.m. Monday. He drove into New York City shortly thereafter, she said.

No one answered the door at the address listed for Tamura in Las Vegas.

Islam, the killed officer, leaves behind two young boys, and his wife is pregnant with their third child, Tisch said.