Story highlights No link seen between assailant and radical Islam, senior law officer says

Zale Thompson swung a hatchet at four police officers in Queens, wounding two

The other two shot him dead, authorities say

A hatchet attack on New York City police officers and two back-to-back attacks on uniformed officers in Canada have raised questions about whether the incidents may have been motivated by the attackers' alignment with radical Islam.

Zale H. Thompson charged at four New York police officers with a metal hatchet Thursday, hitting two of them. The attack is the third on people in uniform in North America in a week.

ISIS, the Islamic State in Syria and Iraq, has recently called on sympathizers in the West to carry out attacks against men and women in uniform. The move raised concerns about such attacks in both the United States and Canada.

Attacks in Canada

Two attackers with some ties to radical Islam, in separate incidents, killed two men in uniform in Canada this week.

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He exited the car, and police opened fire on him. He died in the confrontation.

No direct connection has been found between any of these men and ISIS, though both Canadian attackers had been caught attempting travel to join jihad.

Zehaf-Bibeau had contact with other Canadian Islamists, authorities there have said.

Official: New York case doesn't appear tied to radical Islam

Online postings attributed to Thompson paint a portrait of someone who at the very least held controversial views.

For example, in a comment posted last month to an online video discussing a global caliphate, a user with the name Zale Thompson seemed to justify jihad, "If the Zionists and the Crusaders had never invaded and colonized the Islamic lands after WW1, then there would be no need for Jihad!"

Thompson, a Muslim convert, was killed during Thursday's attack. A law enforcement official told CNN on Friday that the case doesn't look like one of radical Islam.

ISIS has a draw on the disaffected and those who don't feel at home where they are, said jihad expert Richard Barrett of the Soufan Group.

"The general picture provided by foreign fighters of their lives in Syria suggests camaraderie, good morale and purposeful activity, all mixed in with a sense of understated heroism, designed to attract their friends as well as to boost their own self-esteem," he said.

And ISIS constantly cranks the PR machine, making expert use of slick videos and social media.

ISIS has, for an anti-Western organization, been surprisingly attractive to young male recruits from the West as well as to some young women.

More than 100 of the foreign fighters for ISIS in Syria have come from the United States, according to intelligence estimates.

Canadian authorities believe that 130 citizens are fighting in jihad.

Hundreds more have gone from Europe, which is geographically closer to the fight. British authorities place the number of UK citizens fighting in Syria at 500.

Thousands more come from the Middle East and Africa. More than 3,000 have joined from Tunisia, the largest single contingency.

ISIS sympathies

ISIS' global digital reach has terror experts worried about security in the West, especially attacks by lone wolves who may not have any official mission from international terrorists.

And incidents have cropped up to support those fears.

This week, a video turned up of a 17-year-old Australian boy standing with ISIS fighters and threatening to behead Western leaders, including President Barack Obama, and then to fly the ISIS flag over the White House.