When I was working on my MBA we discussed insider trading in my finance classes. Our professor explained to us that the SEC didn't mind people making a little bit of money of insider information but they got pretty upset when you got greedy.
In other words. If you sell 100 shares on insider information and make a couple thousand dollars they won't say anything. But when you make damn near a quarter million like good old Martha did, they are going to teach you that greed is bad.
On part that we discuused is that the SEC uses computer models to search trade records for trades that occur prior to information that has a large impact on a stocks price. Any trades int he two weeks prior (IIRC) that result in large gains, are going to be heavily examined by the SEC.
In Martha's case she sold 3,928 shares of ImClone the day before they went public with the information that the FDA had rejected their drug application. She sold for $58 a share, which netted her $227,824.
That is well above the dollar value that the SEC looks for and well within the timeline that SEC checks.
Rusty