In a picture taken from video provided by the New York Police Department, a man approaches a group of New York City police officers with a hatchet. The man seriously injured one officer before the others shot and killed him, police said.

NEW YORK — A brazen daylight hatchet attack against a group of police officers on a busy New York street was a terrorist act by a reclusive Muslim convert who ranted online against America but had no clear ties to international extremists, the police commissioner said Friday.

Police were examining Zale Thompson’s computer for clues about a motive for the Thursday assault that left one of the officers seriously injured and ended with Thompson being killed by police. Police Commissioner William Bratton said Thompson’s browsing history included organized terror groups, beheadings and the shooting in Canada earlier this week that officials there have called a terrorist attack.

Thompson was not on any watch lists, and officials found no indication he sought any training or affiliation to any groups.

Still, Bratton said he was comfortable calling it a terrorist attack. “This was a terrorist attack, certainly,” Bratton said.

Bratton said investigators were trying to determine whether the attack was planned or spontaneous but believe Thompson was self-radicalized. His father told officials he converted to Islam about two years ago and was described as a “recluse” who had been depressed lately.

Thompson, 32, had once served in the U.S. Navy and had a history of run-ins with the law over domestic violence in California in 2003 and 2004, police said.

Video and witness accounts appeared to leave no doubt that Thompson purposely targeted four rookie New York Police Department officers who were in uniform and on foot patrol in a bustling Queens commercial district.

Moments before the attack, the bearded suspect was seen on a street corner crouching down to pull the hatchet out of backpack before he charged the officers and began swinging the hatchet with a two-handed grip, police said.

At the time, the officers were posing for a photo for a passerby. Without a word, Thompson swung at an officer who blocked the blow with his arm, police said. Another officer was hit in the back of the head and fell to the ground.

As the suspect raised the hatchet again, the two uninjured officers fired several rounds, police said. The bullets killed the assailant and wounded a bystander, police said.

Officer Kenneth Healey remained hospitalized Friday with a head wound. The bystander also was being treated for a gunshot wound to the back. Both were critical.