Intentional or not, the tear gas is what caused the fire.
When all this was going down I was listening to it on police scanner. I heard two cops discussing that they were going to go ahead with the burn out and that it needed to go just like discussed. Soon thereafter the scanner crashed and the house burned down....
http://freerepublic.com/focus/news/2987845/posts?page=599#599
Wanting to end the standoff before nightfall, members of the sheriff's SWAT unit carried out a plan they had devised for a final assault on the cabin, according to law enforcement sources. An officer drove a demolition vehicle up to the building and methodically tore down most of its walls, the sources said.
With the cabin's interior exposed, the officer got on the radio to others awaiting his order. "We're going to go forward with the plan, with the burner," the unidentified officer said, according to a recording of police radio transmissions reviewed by The Times.
"The burner" was shorthand for a grenade-like canister containing a more powerful type of tear gas than had been used earlier. Police use the nickname because of the intense heat the device gives off, often starting a fire.
"Seven burners deployed," another officer responded several seconds later, according to the transmission which has circulated widely among law enforcement officials. "And we have a fire."
Within minutes the cabin was fully engulfed in flames, ending a dramatic manhunt that captivated the nation.