Zeppelin, here's something for you to read for starters:
Battle of Stalingrad - Wikipedia, the free encyclopedia Stalingrad battlefield information Military History Online - Battle of Stalingrad
And
The Battle for Stalingrad is especially good.
There is also the movie "Enemy at Gates". While completely worthless in historical terms, it does provide you with a good visual impression. The initial river crossing sequence is makes you wish you were somewhere else.
The correct term would be not "execution squad" but "blocking detachment". Nothing like a little incentive to put a spring in your step
