Really! You know, I couldn't find anything on which to hang that theory, intriguing as it was. Except maybe the mysterious videotape that shows a long segment of "someone mixing chemicals".
But as his screwed-up mind unfolds on these tapes, I am almost ready to believe that it is LIKELY that he did poison her slowly! He seems just the type.
And if he really does enjoy the suffering of others, what better way to gratify such a hobby than to periodically cause Laci to suffer the pain from the poison?
Well, one thing we do know: we don't know how Laci was killed, just that she was. It could have been poison, among other ways. Certainly, a poisoning death would not leave bloodstains and other evidence in the house--as was the situation in this case.