A surveillance image of a suspect who struck and critically injured an NYPD officer with a hatchet. He was shot and killed by police. (Credit: CBS 2)

NEW YORK (CBSNewYork/AP) — Authorities believe a 32-year-old Queens man Zale Thompson, the man who attacked a group of NYPD officers in Queens with a hatchet before they shot him dead, acted alone. They also said he may have been inspired by this week’s terrorist attack in Ottawa.

“It appears, just from the electronic forensic piece of this, that this is something that he has been thinking about for some time and thinking about with more intensity over recent days,” the NYPD Counter-terrorism Chief John Miller said.

Police obtained a warrant to search 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.

Sources told CBS 2’s Matt Kozar that Thompson had been visiting websites affiliated with Al Qaeda, ISIS, and Al-Shabaab.

A Facebook page linked to Thompson includes a picture of an Islamic warrior and a quote from the Koran.

On YouTube, Thompson appears to have posted a comment advocating “holy war,” saying “If you’re looking for ‘perfect’ Muslims who never make any mistakes in their jihad, then you will be looking in vain,” CBS 2’s Tony Aiello reported.

Thompson was also online “looking at different acts of violence including beheadings,” Miller said.

Authorities also seized a hunting knife as well as another “weaponized ax” from Thompson’s residence after obtaining a search warrant.

Police Commissioner Bill Bratton said Friday at a news conference that he was comfortable calling the incident a terrorist attack.

“This was a terrorist attack, certainly,” Bratton said.

But he also stopped short of including the attack in the list of terror plots against the city since Sept. 11, 2001, saying the investigation was continuing.

Bratton also said it appears to have been a spontaneous attack, but added the fact that Thompson was walking with an ax indicates some preparation.

Security video and witness accounts appeared to leave no doubt that Thompson purposely targeted four rookie officers, police said.