Interesting guide outlining strategies of how to obtain the cooperation of an Inside Witness:
Strategies include, Building a strong case against the witness, which might be based on evidence of transactions other than those involved in the case in which you hope to obtain his or her cooperation. This would include being prepared to rebut his or her anticipated defenses or excuses;
Convincing the witness that you are prepared and willing to move against him or her immediately, with the result that the witness will most certainly be sanctioned;
Offering the witness the opportunity to cooperate to avoid sanction, or more often, to mitigate any penalty that might result;
Assure the witness of confidentiality if the witness demands it. It is better, of course, if the witness would be willing to be identified and testify, but if not, the witness might still provide useful leads.