I doubt that you could find cooberating evidence for any of the above. While Allied units did occasionally shoot prisoners...just as any army of the period did....it was hardly an institutionalized practice or widespread. This sounds more like an attempt by the author to rationalize the behavior of the SS in the West which by all accounts did on more than a few occasions shoot PoW's and do it as an institutionalized practice. One of those "we did it only because the enemy did it first" things.