NCAA Asks For Agents' Cooperation In Eligibility Investigation

Several NFL agents have reported receiving a letter from the NCAA, asking for their cooperation as the investigation into improper benefits for college athletes marches on. I was personally hoping the missives were constructed from cut-out magazine letters, but apparently not:

A person familiar with the letter told The Associated Press that the tone is not threatening and the NCAA is not applying pressure on the agents. But it wants "an environment of cooperation" when NCAA regulations may have been broken regarding contact between agents and amateur student-athletes.
[...]
The NFLPA is encouraging agents and its members to cooperate with any investigations.

How on earth is this going to succeed? Are these guys chatting up college players on the sly going to throw up their hands with sheepish grins and admit to being caught when they're cornered? Is anything short of threats going to make this happen?