Was he a vampire or not? He seemed to be but there are some doubts! Why didnt he kill the last woman, 5th victim? Why was Carl charged for murder? Was it because the vamp wasnt a real vamp? Maybe because they wanted to get rid of him, not sure...
Bumping this thread: this is just how our authorities would do it too (to suppress the truth). I'm no conspiracy buff but it's obvious many in power would sacrifice anyone to keep the truth suppressed and save their necks.
He was indeed a "real, live vampire" (to quote Carl). Skorzeny decided to turn the last victim (Shelly Forbes?) into his own blood bank because the noose was tightening (his picture had been released to the public via Kolchak's paper) and hunting prey in the usual way would be riskier.
The authorities wanted to get rid of any vestige of their incompetence and dishonesty by removing Carl from the scene. Charging him with murder suggests to the public at large there was still some doubt about the true nature of the killer, and absolves their earlier indecision in adopting Kolchak's suggestions.
"I can't lie to you about your chances, but you have my sympathies."