15 seconds to open, plus 5 seconds to pocket

That's how long it took a thief, in full view of CCTV security cameras, to open a glass display case while an accomplice stood lookout.

You can see the CCTV footage released by the authorities below.

In the CCTV camera footage a clean-shaven man wearing a hooded puffer jacket and casual pants, sporting a traditional coppola style flat cap, can be seen viewing the jewels in several display cases at a leisurely pace, along with five other individuals.  Nearby, one of the five, his accomplice, wearing a buttoned sweater and a fisherman's beanie also pretends to be enjoying the exhibition. 

Four of the individuals, two with hats and two without, leave the space viewable by the security camera in one group after only giving passing glances to the objects on display in the exhibition room.  The man with the fisherman's beanie remains, feigning interest in the objects on display before he too moves out of view of the camera's range, standing as a lookout.  

In the next frame of images, after purposely walking towards the middle display, we can see the thief warily working the lock mechanism on the alarmed display case, possibly with some type of burglary tool, though the view of how he unlocks its glass door is blocked by his back, out of view of the camera.  Opening the case takes only 15 seconds.

Glancing back over his shoulder before and after he gains access to the interior of the case, the culprit then reaches in and deftly grabs the brooch and earrings, placing them quickly in his right pocket in just five seconds.  He then closes the glass door on the case and exits in the same direction as the four earlier individuals. 

It is not very clear whether or not the four other individuals pictured in the CCTV  footage had any role in the event.  Nor is it unusual for patrons to wear hats in Italian museums during bouts of colder weather.  What is clear, though, is that hats used as disguises can be quickly removed and hooded puffer jackets can be flipped up or discarded with ease, allowing the thief and his accomplice to rapidly change their appearance, making them less identifiable.

This change-up can be seen in the footage stills taken of the two suspects.

In the top image, the lookout has donned a red puffer jacket which now covers or has replaced his earlier buttoned sweater.  

As the pair depart, the lookout exits with his hands stuffed in his pockets while the man who removed the objects from the case inside the Doge's Palace now has his hands free and appears to be talking on his cell phone.