Diving into a tar pit to find a murder weapon

Sergeant David Mascarenas is an underwater diver for the police in the American city of Los Angeles. He's responsible for collecting weapons, bodies and other evidence from the waterways of the city. But when a murder enquiry began, he faced a new and quite dangerous challenge: retrieving evidence from the La Brea tar pits. These are pre-historic pits of bubbling tar right in the heart of the city. He told Jo Fidgen about his work. (Picture credit: LAPD.)