Police body cams are designed to record the 30 seconds before a cop actually activates their body cam, a fact which apparently escaped LAPD officers who recorded themselves appearing to plant cocaine in a suspect's wallet:

CBS2, which got access to the tapes, breaks down the alleged planting of drugs:

[Officer Samuel] Lee is seen searching the suspect. He testified in court, as in the police report, that the cocaine was found in Shields' left front pocket. But the videos shows a different story. In video from another angle, LAPD Officer Gaxiola picks up Shields' wallet from the street and shows it to Lee, who points to the suspect as if to say it's his. He then puts it back down, steps to the street, bends over and picks up a small bag with white powder. It eventually tested positive for drugs. Gaxiola goes back onto the sidewalk, picks up the wallet, motions to Lee and appears to put the bag into the wallet.

[CBSLA]

The officers maintain that the drugs had fallen out of the suspect's pocket, and as Reason notes, there may be an alternate explanation:

It may well be a situation where the officer was re-enacting "discovering" the drugs for the camera and didn't actually plant drugs on an innocent man. That was the claim out of Baltimore. That's still a terrible, deceptive practice that needs to stop immediately because it jeopardizes everything else about the arrest. You cannot "recreate" the discovery of evidence and expect people to reasonably believe everything else is real.

[Reason]

This isn't the first time cops have unwittingly filmed themselves while appearing to plant evidence — Baltimore cops got caught two separate times earlier this year.