Police are on the lookout for two thieves they say have gone on a mail-stealing spree across San Francisco. According to Fox 2, the man and the woman appear to have obtained a USPS master key — the thing that allows mailmen to gain access to apartment building lobbies and open mailboxes — and are using it to steal credit cards, passports, and other valuable documents.

Video surveillance from one building on Van Ness Avenue depicts the alleged criminals at work during what is one of the three times they are accused of striking that very same building. "I was amazed they were totally relaxed [when] they walked in," resident Caxton Rhodes explained to the channel. "[They] knew exactly what they were doing especially when they're carrying — they both have cups of coffee! These guys had stolen [a new credit card] on Thursday, well, on Saturday, they charged like $5000 in charges to local businesses."

What makes this case so crazy is that unlike with your run-of-the-mill package thieves, possession of the USPS master key means this duo can physically enter multi-unit apartment buildings — so even things left inside by your neighborhood deliveryman are still vulnerable.

Officials say buildings in Japantown, Cow Hollow, and Fort Mason have all been targeted, and that they can't immediately do anything about it  changing all the vulnerable locks would cost at least $200,000 and will take some time. Mailboxes in the 94109 zip code are believed to be specifically at risk.

"The mere possession of one of those keys is a federal felony, [and the] potential penalty is up to 10 years in federal prison," U.S Postal Service Inspector Jeff Fitch told Fox 2.

Somehow, we don't think that fact will be much of a deterrent. But hey, at least they're not stealing entire mail trucks.

Related: Video: Thief Steals Child's Birthday Present, Gleefully Dances Away