Martha Stewart didn’t go to prison for securities fraud. She went to jail for lying to the FBI when they initially talked to her about her case. There were no charges against her at the time.
Again, they did cooperate, and when they did, they were inconsistent in what they told the police and with what the police later learned to be true. Maybe that leads to a case, maybe not, but it definitely should not be ruled out. I know law enforcement have not ruled it out, they have said they haven’t decided on whether or not any charges will be made.