The promise of Snapchat was broken in October 2013, when the messaging app admitted that the premise of its service — self-destructing images and videos that would never come back to haunt the user, or (let's be honest) sexter — was compromised by the long arm of the law.

Under the Electronic Communications Privacy Act, Snapchat must comply with search warrants for pictures and videos from U.S. law enforcement agencies.

But while online privacy activists have focused on search warrants aimed at Snapchat's servers, the San Francisco Police Department has found another way to use the app to its advantage.

According to a recent search warrant request, SFPD's "Instagram Officer," Eduard Ochoa, was cruising Snapchat on Oct. 11 when he recognized the profile of a Bayview resident on felony probation. Ochoa watched three of the man's Snaps, saw a gun, and immediately went to the offender's house to conduct a probation search. Ochoa didn't find the firearm, but asked for, and was granted, a search warrant for the man's residence, vehicle, and DNA.

Ochoa, who earned the title "Instagram Officer" in a recent appellate court ruling, is adept at using social media in investigations. The court ruled that an Instagram photo Ochoa had printed out was permissible as evidence in a case against a juvenile.

In this case, Ochoa didn't have to serve a warrant to Snapchat for a copy of the image in question — he just described the disappearing picture in an affidavit. (It's unclear from the warrant, but it's possible Ochoa also presented the judge with a screenshot of the image — another workaround for Snapchat's privacy settings.)

That's troubling to Nadia Kayyali of the Electronic Frontier Foundation.

"This is incredibly open to abuse and human error," Kayyali says. "Police officers scanning Snapchat are going to see what they're looking for. This shouldn't be allowed."

A fair sentiment, but as long as it is allowed, best to think twice before you snap.