I hadn't heard of the app before now, but I'm not finding much sympathy for users of a system built on the premise that they should not have access to data on their own device.

Anyway, a clarification of the headline: not only 'unopened' snaps, but also those that have not yet been opened by all nominated recipients. So if a law enforcement agent can have themselves invited into a Snapchat circle they can take advantage of that fact to persist the image on the server until it is legally demanded.