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.
Where in the world do you get the idea that Lay was "still buying shares and never sold them"?
Between August and October, 2001, as the company stock was plummeting, he sold 918,000 shares worth $70 million!