The city thinks there's a good chance police will catch a vandal who threw a fist-sized rock at a photo-radar van in Edmonton earlier this month.

This is the rock a vandal threw at a photo-radar van. (CBC) Dennis Tetreault, supervisor for the city's office of traffic safety, said the rock hit the van's fender but could easily have gone through the open window and struck the man inside.

Such acts of vigilante vandalism are not uncommon, he said.

"We're having attacks on our vehicles on a weekly basis," Tetreault said. "Whether that be eggs or coffee cups or slurpee cups. We've had rocks thrown at our cars before. We've had windows shot out with pellet guns. We've had our operator sitting at a site and had five or six pellets shot at the front windshield."

In this case, someone passing the van at 80 km/h threw a two-pound rock the size of a baseball. Simple physics shows the force of the impact could have seriously injured or killed the man inside the van.

"That guy is a human being," Tetreault said of the photo-radar operator. "He's got a family. He's just trying to support his kids and to make a living.

"What seems to be just a harmless prank could actually be fairly serious. Whether you agree with (photo radar) or not, this is certainly not the way to disapprove of the system."

But Edmontonian Maurice Hilarious said if the suspect is caught, he would donate $50 towards the vigilante's legal defence. And he wants others to pitch in.

"He wanted to make a statement. Yeah, there was some damage. I'm not impressed with that but really what options do you have left to protest this anymore? It's clear there aren't many."

Tetreault said he doesn't appreciate such comments.

The dashboard camera in the photo-radar van captured video of this SUV, which police say is a dark-blue or black 2006 Pontiac Torrent. (Supplied) "I think it's kind of repulsive, when you think of someone collecting money to support vigilantism."

All photo-radar vehicles are equipped with dashboard cameras. In this case, the vandal removed the licence plate from his SUV, but the video shows what police think is a 2006 Pontiac Torrent, dark-blue or black, with a trailer hitch mount on back and damage on back fender.

"We're hoping that the photographs get out and the public can identify this guy," Tetreault said.

In June 2002, Robert Stanley, 75, was killed after a rock was dropped from an overpass onto the school bus he was driving on the Whitemud Freeway. The two teenagers convicted in his death received six-months of house arrest, 18 months of probation and 240 hours of community service.