US Attorney Preet Bharara just sent chills through hedge funds and Wall Street trading desks.

"We're not finished," the prosecutor who has charged 20 people with insider trading said.

"How pervasive is insider trading? The answer is we don't know. But we intend to find out," the prosecutor said.

He also issued a call for anyone involved in insider trading to come forward.

"You should knock on our door before we knock on yours," he said.

Once again, the investigators in the case used hardcore criminal law enforcement techniques to catch alleged insider traders. Phones were tapped and cooperating witnesses wore wires to meetings. Even attempts by the targets of the investigation to avoid surveillance by using prepaid cell phones were apparently foiled.