A gunman armed with an AR-15-style rifle burst into the lobby of a Manhattan skyscraper Monday evening and began firing, eventually killing four people, including a police officer, and creating chaos in the bustling Midtown office area during rush hour.

The gunman killed an off-duty New York City police officer working security at the 44-story building, and three other people, as he made his way through the lobby and then to the office of the building’s owners, before killing himself, officials said.

The shooting, at 345 Park Avenue, which is owned by Rudin Management and home to high-powered companies like Blackstone and the National Football League, set off chaotic scenes that spilled into the streets of Midtown.

Here’s what we know about the incident’s chain of events.

The gunman opened fire in the building’s lobby

At 6:28 p.m., multiple 911 calls came in about a shooter inside 345 Park Avenue, Police Commissioner Jessica Tisch said at a news conference on Monday night.

The gunman pulled up in a black BMW and stepped out of the car carrying an AR-15-style rifle. He entered the lobby of the building and immediately opened fire on a New York police officer. He struck another woman and man and sprayed the lobby with gunfire as he made his way to the elevator, where he shot a security guard who was taking cover behind a desk.

A woman came out of the elevator, and the gunman let her walk past him unharmed, Ms. Tisch said. Then he went up to the 33rd floor, Rudin Management’s office, where he fatally shot a woman before shooting himself.

The tower is home to several financial institutions like the investment giant Blackstone, and the accounting and financial advisory firm KPMG, as well as the National Football League. It is owned by Rudin Management, one of the oldest real estate firms in New York.

A New York police officer was among the victims

Four people were killed, including the police officer, whom officials identified as Didarul Islam, 36. Mr. Islam was assigned to a Bronx precinct and was one of two officers working a paid security detail at 345 Park Avenue, Ms. Tisch said. Mr. Islam, an immigrant from Bangladesh, was a three-and-a-half-year veteran of the police department, officials said. He had two children, and his wife is pregnant with their third child.

“He was doing the job that we asked him to do,” Ms. Tisch said of Mr. Islam. “He died a hero.”

Another man and two women were also fatally shot, and a man was critically wounded, officials said. The police did not release details about the other victims. The shooter died of an apparently self-inflicted gunshot wound, Mayor Eric Adams said.

The gunman drove across the country to Manhattan

Officials identified the shooter as Shane Tamura, a 27-year-old man from Las Vegas. He had driven across the country from Nevada, and arrived in the city just hours before unleashing mayhem in Manhattan, they said.

Mr. Tamura had “a documented mental health history,” Ms. Tisch said, without elaborating, adding that he appeared to have acted alone. He was licensed to carry a gun in Nevada, and his motives were still unclear, she said.

Investigators searched the gunman’s vehicle at the scene, and inside found a rifle case with rounds, a loaded revolver, ammunition and magazines, as well as a backpack and medication prescribed to Mr. Tamura, Ms. Tisch said.

Mr. Tamura’s car was recorded passing through Colorado on Saturday, then Nebraska and Iowa on Sunday, before he arrived in New York City on Monday afternoon, officials said.