Authorities in California say arson is the cause of a wildfire that has burned nearly 60,000 hectares of land near Los Angeles.
State and federal officials made the declaration Thursday evening. The fire, which also destroyed 64 homes, is the largest wildfire in the history of Los Angeles County.
Authorities say they have launched a homicide investigation because of the deaths of two firefighters, Ted Hall and Arnie Quinones, who were killed Sunday when their emergency vehicle plunged down a steep mountain road.
Hundreds of firefighters gathered at the fire command post Friday to honor their fallen comrades. A public memorial will be held September 12 at the baseball stadium for the Los Angeles Dodgers.
Investigators are focusing on an area north of Los Angeles as the possible epicenter of the fire, which has burned for about 10 days. Officials say the blaze is now 42 percent contained.
By Thursday, safety officials had lifted all evacuation orders for residential areas, allowing people to return to their homes.
The fire also threatened a historic observatory north of Los Angeles, but a firefighting force atop Mount Wilson managed to keep the flames from reaching the site and critical communication towers on the mountain.
Some information for this report was provided by AFP, AP and Reuters.