1. What started the California wildfires?

Investigators are searching charred rubble left by the deadly Camp Fire for clues. The fire caused at least 56 deaths, with hundreds more missing, and destroyed more than 10,000 homes and businesses.

But the search has been slowed by the ferocity of the blaze. Above, Paradise, Calif.

One line of inquiry, an investigator told us: Was the culprit an electrical problem like a fallen power line? Officials have found that the main electric utility in the region was responsible for at least 17 of 21 major fires in Northern California last fall. And the utility declared that it could face crippling liability bills, potentially leaving customers on the hook for billions.