why was Burt on the list of those who killed Peter?
At the end of one of the "who killed Peter?" episodes, the narrarator says "Jessica did not kill Peter. One of the following did...", and five different characters were shown, Burt being among them. But Burt was the first one to know of the murder, and his reaction was shown. He came to Peter's apartment, saw him dead, and was shocked. He shouldn't have been one of those suspects.
Sure, he could have been the killer in the same way Chester was, with him losing memory, but at the time viewers wouldn't have known that the killer had a memory problem.