New York shooting: Everything we know as crazed gunman kills 4 including hero cop

A man with a rifle killed an off-duty police officer and three other people before taking his own life yesterday.

The gunman - named in a press conference as Shane Tamura - brazenly struck at an office block in Manhattan, New York City, home to large companies, such as banks and the National Football League (NFL). Law enforcement officials are working to unravel what took place and why this location may have been targeted in the Big Apple.

The city had recently announced it was on pace to have its fewest people hurt by gunfire than any year in recent decades. However, it is now mourning those killed, including "hero brother" police officer Didarul Islam. Colleagues paid tribute to the 36-year-old man, whose wife is pregnant with their third child, at a press conference last night.

Below The Mirrorhas outlined some of the key things to know as New York City fondly remembers the four innocent souls murdered in the sickening attack.

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READ MORE: New York UPDATES: Didarul Islam among four dead in 'pure evil' mass shooting

What happened?

A man - thought to be Tamura - exited a double parked BMW with an M4 rifle and then walked toward the building on Monday evening, according to surveillance video.

He quickly opened fire on the NYPD officer as he entered the building before shooting a woman who tried to take cover, police Commissioner Jessica Tisch said at a news conference on Monday night. He then started "spraying" the lobby with gunfire.

The man went to the elevator bank and shot a security guard who was taking cover behind a security desk and also another man in the lobby, Ms Tisch said.

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

What do we know about the gunman?

Police identified Tamura of Las Vegas as the gunman, although his motive and reasoning for targeting the building is not immediately clear. Tamura had a "documented mental health history," Ms Tisch said.

His vehicle had traveled across the US through Colorado on July 26 and then Nebraska and Iowa on July 27. It arrived in Columbia, New Jersey, as recently as Monday afternoon, before making it to New York City, she said.

Officers found a rifle case, a revolver, magazines and ammunition in his car, Ms Tisch said. No one answered the door to reporters at the address listed for Tamura in Las Vegas.

Who were the victims?

Didarul Islam, 36, had served as a police officer in New York City for three-and-a-half years. He was an immigrant from Bangladesh. Mr Islam was married and had two young boys, Ms Tisch said. His wife is pregnant with their third child.

The names of the other victims, along with a man who was seriously wounded and remains in critical condition, have not yet been released.

Where did the shooting happen?

The shooting took place at 345 Park Avenue, a commercial office building in a busy area of midtown that is just a short walk north from Grand Central Terminal and about a block east of St. Patrick’s Cathedral.

The building's tenants include the NFL and Rudin Management, as well as finance companies KPMG and Blackstone. It also includes the consulate general of Ireland.