Responding to the deadly attack in New York Tuesday afternoon, Philadelphia Police Commissioner Richard Ross asked city residents to remain alert and report suspicious activity.
"We don't think we are in any more jeopardy than anyone else, but we don't take it for granted," Ross told reporters at Police Heardquarters at Eighth and Race Streets in Center City.
"I just urge people to do what we've been asking for years now, that is if you see something suspicious, let us know," Ross said.
"If you see a change in behavior in individuals, please don't wait until the last minute and please don't have that on your conscience at a later time, to say that I should have called someone," he said.
Authorities said Sayfullo Saipov, 29, drove a rented truck onto a bicycle path near the World Trade Center memorial, killing at least eight people and injuring several others. New York Mayor Bill de Blasio called it "an act of terror, and a particularly cowardly act of terror aimed at innocent civilians."
Saipov was cited in Pennsylvania for traffic violations in 2012 and 2015.
He was stopped by a state trooper on Aug. 25, 2012 in Palmyra Township, which is east of Scranton, court records show. He pleaded guilty that November to one violation and a second citation was withdrawn.
On Mar. 26, 2015, he was stopped by local police in Mount Holly Springs Borough, which is southwest of Harrisburg. He pleaded guilty that April to two violations.
In both years, his home address was listed as Paterson, N.J.
"We will continue to be vigilant in this city," Ross said, "both protecting those soft targets, as this one was, the best that we can."