NEW YORK CITY -- Investigators are trying to determine why a man attacked a group of New York City police officers with a hatchet, CBS New York reports.
Police obtained a warrant to search 32-year-old Zale Thompson's computer for clues about Thursday's daytime assault, which left one officer with a serious head injury.
Thompson's activity on social media indicated he was a convert to Islam and included rants about injustices in American society and oppression abroad but offered no clear evidence of any affiliation with terror groups, police said.
Security video and witness accounts appeared to leave no doubt that Thompson purposely targeted four rookie officers, police said.
The attack occurred at about 2 p.m. Thursday while the officers were standing together on foot patrol in Queens.
Without a word, Thompson swung at an officer who blocked the blow with his arm. Another officer was hit in the back of the head and fell to the ground.
"Nothing was said at the time of the assault. The suspect was described as having charged at the officers," Police Commissioner Bill Bratton said at a news conference Thursday.
As Thompson raised the hatchet again, the two uninjured officers drew their weapons and fired several rounds, killing Thompson and wounding a female bystander, police said.
Moments before the attack, Thompson 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.
A bloody hatchet, about 18 inches in length, was recovered.
Asked if the attack could be related to terrorism, Bratton didn't rule it out. He cited the fatal shooting of a soldier in Canada earlier this week, what officials there have called a terror attack, as reason for concern.
"This early on, we really cannot say yes or no to that question," Bratton said Thursday.
Thompson graduated from the College of New Rochelle in 2008 and worked in information services at the college until 2012.
Previously, he was discharged from the U.S Navy for misconduct and has a criminal record in California for domestic assault.
On YouTube, Thompson appears to have posted a comment advocating for "holy war."
CBS New York reports that he wrote, "If you're looking for 'perfect' Muslims who never make any mistakes in their jihad, then you will be looking in vain."
Officer Kenneth Healey, who was slashed in the head, was taken to Jamaica Hospital Center in critical but stable condition. The second officer, Joseph Meeker, was also taken to the hospital for injuries to his arm.
The female bystander who was accidentally struck by a police round was taken to Jamaica Hospital Center.
Authorities said she was about half a block down the street from the incident when she was injured.
Bratton said all the officers involved are recent graduates of this summer's police academy class.