A man is attacking and burning homeless people while they sleep in San Diego, authorities have announced.

Two men were killed in the attacks, which took place in 24 hours, and one is fighting for his life in a local hospital, CNN reports.

Police received 911 calls on Sunday morning from witnesses claiming a homeless man was on fire along train tracks in the city. He was burned so severely that officials were unable to tell if he was burned before the attacks, San Diego Fire-Rescue Department Spokesman Lee Swanson told the station. Another middle-aged man was reported fleeing from the scene carrying a gas can.

One of the two victims died at the scene.

“These are very, very violent attacks,” San Diego Police Captain David Nisleit told reporters on Tuesday.

Violence against homeless persons is somewhat common in the city, as two brothers and one female teen were accused of fatally beating a homeless man in El Cajon early this year, CNN reports. In 2011, Kelly Thomas was killed after being beaten by two police officers, who were acquitted from second-degree murder charges in three years later.