Honest question:

If you have no evidence, then why do you believe it?

Circumstantial plus expecting the worst.

A company and founder with such an extensive list of publicly known misdeeds (starting with Facesmash), chances are that there are many skeletons left to uncover. Setting a precedent is no unknown course of action.

It's not much to go by, but I am a commenter on HN, not a lawyer and Occam's razor doesn't disagree either.

Because it is extremely unlikely she knew everything. Based on her book, she was last to learn quite a lot of ugly stuff she reports on - they told her only when they had to.

And she left long time ago. It is even more unlikely that the company magically became clean after her leaving.