The Fort McMurray wildfire MWF-009, which came to be known across Canada as "The Beast," was not ignited by a lightning strike, and police are now asking for the public's help to determine whether it was the result of a criminal offence.

Provincial wildfire investigators have established that the fire was most likely the result of "human activity."

The fire was first sighted about 15 kilometres southwest of Fort McMurray by an airborne forestry crew on May 1.

Over the next two days, the wildfire grew rapidly. On May 3, pushed by high winds and fuelled by tinder-dry conditions, the fire raged into the city itself and forced more than 80,000 residents to flee.

RCMP focusing on Horse River Trail system

Police have not yet determined how the fire started, but want to speak with anyone who was in the Horse River Trail system between April 29 and May 5.

Cpl. Hal Turnbull said this area is popular with hikers and ATV riders.

"It's not an area that's remote and isolated, it's an area that's frequently accessed by the individuals who reside in and around the Fort McMurray area," Turnbull said.

Because of the unique scope and magnitude of the fire, Turnbull said, it's only natural that police would investigate the cause. 

This investigation needs to be done now, he said, before any physical evidence may be lost.

"It's not that we have any suspicions or beliefs that there was criminal activity, it's just a natural cause that people will say, 'Have you looked at whether arson was a factor? Or whether any criminal activity may have occurred in the area which would have caused the fire?' " Turnbull said.

"At the end of the day, we want to be able to say, 'Yes, we did so in a timely fashion, and here are the results of our investigation.'"

Anyone with information is asked to call the RCMP's dedicated toll-free wildfire investigation phone line at 1-844-620-9826.

The fire destroyed some 2,400 buildings in Fort McMurray.

In the six weeks since it started, the fire has moved north and east of the city, and in recent days has shown little growth. It is now more than 80 per cent contained.

The fire has burned about 590,000 hectares and has a perimeter of about 1,000 kilometres.