SWAT officers in the cabin standoff with murder suspect Christopher Dorner decided to use highly flammable "hot gas" canisters as a last resort after other efforts to persuade Dorner to surrender failed, according to law enforcement sources.

Officers made the decision to use the canisters, which caused the cabin to catch fire, Tuesday as the sun was setting and authorities worried about dealing with Dorner at night in the remote Big Bear area, said the sources who spoke on the condition of anonymity because the investigation was ongoing. Dorner had continued to fire on officers, and they feared more deputies would be hurt or killed, they added.

Authorities had chased Dorner into the cabin on Seven Oaks Road on Tuesday afternoon amid a massive gun battle in which one San Bernardino County deputy was killed and another badly wounded.

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Law enforcement officers lobbed conventional tear gas into the cabin, but when Dorner failed to emerge they used CS gas canisters, a more intense weapon known to start fires, and sent in a demolition vehicle. Dorner is believe to have died inside, though it is unclear if the fire caused his death.

San Bernardino County Sheriff John McMahon said deputies did not purposely burn down the cabin. He said they deployed the CS canisters after they were left with no other options.

"I can tell you it was not on purpose," he said. "We did not intentionally burn down that cabin to get Mr. Dorner out."

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McMahon praised the deputies involved in the standoff. "It was like a war zone, and our deputies continued to go in the area .... Our deputies are true heroes."