I've always wondered if at some law enforcement agencies, there are unofficial guides on how to make sure a memory card has been wiped. Back in the day of film cameras, taking the film or damaging the camera to ruin the film might have been enough. With digital cameras, even forcing the photographer to do a memory card format was not sure-proof, if the photographer knew how to run disk-recovery software. I remember at least one story where a police officer either confiscated a photojournalist's memory card or made the photographer erase it...but the photojournalist had a dual-card camera in which all the photos were auto-copied to.

With all those subtleties and complexities about digital camera technology (SLR or smartphone cameras), it probably does make sense to a malicious cop to just take and "lose" the camera. But technology continues to be a step ahead...