Canada attack raises "lone wolf" worries in U.S.

Following the attack in Canada, American law enforcement officials are most worried about potential copycats in the U.S., reports CBS News correspondent Bob Orr.

A homegrown violent extremist, a so-called "lone wolf," may decide to strike out in the name of the Islamic State of Iraq and Syria (ISIS) or another terror group.

The threat from self-radicalized Americans is not new, but in recent weeks ISIS has cranked up a propaganda campaign urging attacks on U.S. and Western targets wherever and whenever possible.

ISIS praised the Ottawa shooting as an example of what followers can and should do.

Sources said the FBI is watching a number of Americans right now, perhaps a few dozen, who have tried to go to Syria or have already come back from there.

Those who have shown a desire to join the jihad are under varying degrees of surveillance and investigation.

Meanwhile intelligence officials continue to scour the background of the Canadian gunman.

Records show he traveled to the U.S. at least four times between 2010 and 2013, but officials attach no significance to those trips.

Sources said there is nothing in his background connecting him to any threat against the U.S. and nothing to indicate he had any strong connections to any global terror group or cell.