First, welcome to the site.
This looks to be a Roux-underlever drilling with the shotgun barrels both 16 gauge and the rifle barrel the old 9.3x72R "forsterpatrone", made in Suhl and proofed in November 1923. Krupp steel barrels all around.
Some of the other members here will have better information on the actual mechanics who made the gun. The mechanics all had individual marks they stamped on it to record their part of the work. It appears to be what we in America call a "guild" drilling. That is to say, one large company did not make the entire gun from start to finish but rather various small shops specializing in one part or another took part in making the gun as more or less a collective effort, usually in response to an order from a retailer for a certain number of guns of certain quality and chamberings.
You will have to show us more of what was done to de-weaponize the gun. It appears they drilled a hole in the rifle barrel's chamber and it appears, but is unclear, that they did something to the standing breech, the vertical face where the rear ends of the cartridges were held when the barrels were closed. Also, could you please advise whether the screws for the action plates on either side are missing, or that you removed them for some reason before photographing. Finally, are the insides of the action - the leaf springs and other parts that drive the hammers - present, or did the police take them, too?
The reason for these questions is that, depending on how thorough the police were when de-weaponizing the gun, it may not be possible to repair it, or it may not be economically reasonable to repair it.
It was a fine gun when it was built. Similar guns, but in working order, sell for between $1000 and $1500 in America, depending on their condition (particularly the condition of the barrels).
