A U.S. forensic video analyst says investigators in Boston may follow the example of Vancouver police, analyzing photographic evidence to track down who is responsible for the explosions at the Boston Marathon on Monday.

Vancouver Police used new image analysis technology to create a searchable database of 30,000 YouTube videos and Facebook images to identify the Stanley Cup rioters.

"Vancouver is actually the model for these kinds of investigations going forward," said Grant Fredericks, who led a team of 52 analysts in processing video collected during the riot investigation.

"The most prolific source of evidence available for police generally comes from video evidence," said Fredericks.

More than 1,000 law enforcement officers from different agencies have been assigned to the Boston investigation. Fredericks says the Law Enforcement and Emergency Services Video Association has already been contacted by investigators.

"Vancouver set the standard, and I know Boston is looking at that standard," he said.

"The FBI has already been in contact with LEVA. They are interested in the Vancouver model. They want to see how well it worked, what technology is available, and they want to look at whether it's an option for them with this investigation."

Authorities in Boston are now asking witnesses to share any photos and videos taken from near the finish line to help investigators gather clues. Fredericks said that kind of evidence is key.

"There is no doubt that there are hundreds of people walking around with video images of the suspect or suspects who placed those explosive devices," he said. "They will be pursuing witnesses all around the world."

The challenge, Fredericks said, is tracking down all the race participants and witnesses who have already left the United States.

Runners returning to Vancouver on Tuesday reported police at the Boston airport were asking departing passengers if they had any video or pictures on their cameras or phones that may have captured some photographic evidence.

Three people were killed and more than 170 were wounded when two devices exploded near the finish line of the annual race on Monday.