LOS ANGELES — A report of a burned pickup truck on a Southern California mountain road is being investigated amid a manhunt for a fired Los Angeles police officer suspected in three murders. TV news helicopters have shown a helicopter drop a rifle-equipped team onto a mountain near Big Bear Thursday afternoon. San Bernardino County sheriff’s Deputy Zach Beckum says a pickup fire was reported but there has been no sighting of suspect Christopher Dorner. Beckum also says local schools are on lockdown. A massive manhunt is under way for Dorner, who allegedly killed a former police captain’s daughter and …