Lay and Skilling knew so that makes them accessories and just as bad.
If I propose we rob a bank together but I know how to crack a safe and you don't but you take half the money anyway you are still guilty.
All three are/were scum.
Lay was not aware - Skilling purposely fudged his presentations to the board to represent matters as being on the up-and-up.
As the house of cards was coming down, Lay was still buying shares and he never sold them.
Lay was derelict in his duties as CEO, but it is hardly clear that he actively particpated in Fastow's schemes. His crime was not asking enough questions.
Lay's situation was not analogous to a bankrobber in league with a safecracker.