やはり貴様か・・・！
For some reason, the Waffen-SS of the Last Battalion were not a military group but an urban gang, and it was up to us Ninja Turtles to deal with them. The Hauptsturmführer's work was easy to identify, as there weren't many others running around with Broomhandle Mausers these days. Oddly enough, Dok wasn't actually doing anything evil, just researching at a local library.
It had been replaced as a service pistol even by WWII, although some officers (such as him) still had personal ones. As the only confirmed Werwolfes are him and Ms. Rip-Van, we don't know anything about how they're spawned, so for all we know he may have been a soldier for decades before that. Interestingly enough, the powers they are seen to have seem to relate to firearms: Ms. Rip-Van's dancing musket ball and the Hauptsturmführer's ability to make two long-barreled Mausers look like one normal piece when holstered （笑）. (Speaking of extensible barrels, DM had to make a similar excuse so that typical slugthrower rifles (exemplified by the Czerka Adventurer) can double as BAW E-5 Droid Blaster Carbines due to the changes he's made to the plot.) Tangentially, I'm also amused by the fact that humans like Walter can chop up people with mono-wire, while vampires (there's one who shows up later on, not to spoil anything by saying where) can chop up skyscrapers. There's also the fact that Walter is a gunsmith, yet he fights exclusively with mono-wire. (I've thought of a logical reason for that, but that's because he was working to make Arucard the best foe he could for the Last Battalion.)
Admittedly, there are Mauser variants chambered in modern calibers, so his work might not be identifiable by the ammo and brass left at the scene if he uses one of those. However, each firearm has a distinct pattern of marks that it leaves on each bullet from the rifling in the barrel. I think I may have heard that it's possible to determine the model as well, but I failed to find confirmation on that; still, they would be able to tell that all of the rounds came from the same two weapons, making it easier to link it to a specific person.
Since they're German, I assumed it was an abbreviation of the German word. I don't know whether they use such an affectionate term in German, but I don't imagine Hirano does either. (The dwarf is known as "Chef.") Using German words can lead to some odd things; this one is the same as an Ork word, and "Death Korps" is a bit of a false friend. . . .