Some good background here. An excerpt:
Perhaps it is sometimes possible to trade on insider information and have those trades go unnoticed amid a sea of non-insider trades. But if the non-public information you’re trading on is likely to tank the stock price by more than 90%, and your trades are going to make up about 15 times the stock’s typical daily trading volume, and your close associate sits on the company’s board of directors, it is probably not best to assume that your trades will get lost in the shuffle.