So Hetherington was so drugged "out of his right mind" that he can't be sure that he did not commit the crime, but he still knows that he did commit the crime.
This sentence is false.
That's more than I know.
If you're suggesting it's impossible to be so drugged that you don't remember stuff, I'd argue that drunks often experience blackouts.
Whether or not Hetherington ever took drugs I don't know, it's an allegation by someone who claims to be his daughter ... I just posted it for the sake of the discussion.