An interesting thing I noticed - in the scene where a man is about to become yet another victim of "Der Hei" ;-), it seems there was a 3rd person in front of the camera, snapping their fingers, perhaps giving "The Shark" a signal to shoot (the following is a JavaScript animation):

P.S. Me & my wife love these krimis! ;-) We went to Germany for our honeymoon - we were touring the famous Ludwig II's castles. One night, just out of curiosity, we turned on the telly in the gasthaus we were staying in, and - what a surprise - they were showing a Wallace double-bill, "Das Gasthaus an der Themse" & "Der Hund von Blackwood Castle!" We had a lot of fun that night... (c: