Yepp, that has been my gutfeeling all the time that Frank Thorogood had to be involved in some way. Anna was also indicating something similar in her book. It's now a few years since I read it so I cannot remember exactly what she said. I do not believe for one single second that Brian died of natural causes.
Don't know why, but all of them always felt suspect to me, Thorogood, Wohlin and Keylock, but no conrete idea. For me they all were involved, what the hell ever they had to do with it.