Maybe your idea of a typical crime scene is set in a ransacked hotel room or a dark alley.

But Los Angeles Police Sergeant Dave Mascarenas doesn't investigate crimes on land. He heads up the LAPD's dive team, and one of his most harrowing adventures is the subject of this week's Criminal podcast, hosted by Phoebe Judge.

Criminal is a podcast recorded at WUNC.

Eric Hodge talks with Criminal podcast host Phoebe Judge about this week's episode. It tells the story of a policeman who made a dangerous dive into the La Brea tar pits searching for police evidence.

Diving for the LAPD isn't like scuba diving in the clear open water off the southern California coast. Often these divers venture into sewers, dams or other areas with low visibility looking for dumped bodies, drugs and weapons. The water is often cold, and sometimes they even go into underwater caves.

But in this episode, Mascarenas details the time he dove in the La Brea tar pits. These pits have existed for tens of thousands of years in the heart of Los Angeles. They're large, hot lakes of tar with bubbling methane gas.

"The thing that makes them a rather big tourist attraction is that tens of thousands of years ago, big animals would wade into these things and get stuck," Judge says. "Woolly mammoths and hyenas. They have something there that's dated as 46,000 years old. It's this wild place."

LAPD detectives thought the pits could hold evidence from a high profile 2011 murder case and tapped Mascarenas to dig around.

"We pretty much do everything in our department because we try not to say no to an investigation if at all possible because then we're sending a message that, hey this is a good idea to dump evidence here," Mascarenas said.

It was up to Mascarenas to take the risk and plunge into the dark unknown. After all, he was the head of the team and also older than the others.

Still, the LAPD took as many precautions as possible. Mascarenas wore a helmet and protective suit and also had a way to get air pumped down to him. The police placed fire trucks on standby with hoses ready to spray if a fire started or to clear the top layer of tar off. And they had row boats stationed to yank Mascarenas out if he got stuck.

To help him move around, Mascarenas was connected to another team member using a pole, and he also had sonar communication.

"Because he couldn't actually see what he was looking at—it's tar—there were people radioing to him saying put your hand three inches to the left and feel around," Judge says. "We'll hope it's not an alligator bone that you find but rather a piece of evidence."

Mascarenas said some parts of the tar pits felt soft like pudding.

"Other parts you touched and you immediately got stuck, and it was like a cartoon commercial where your gloves would stretch like a foot till it'd finally give way."

The dive turned out to be successful with Mascarenas recovering several pieces of evidence. It still wasn't easy though. What was supposed to be a nine-minute dive took more than an hour, and he had a few close calls.

You can hear the rest of the story today at the Criminal website, or by tuning in to WUNC on Sunday afternoon at 5:40 p.m.