“Greenberg started speaking with investigators when he realized it was his only path to leniency in the face of considerable evidence against him . . .”

https://guidelines.ussc.gov/gl/§5K1.1 (bad link, so)

§5K1.1 - SUBSTANTIAL ASSISTANCE TO AUTHORITIES (POLICY STATEMENT)
Upon motion of the government stating that the defendant has provided substantial assistance in the investigation or prosecution of another person who has committed an offense, the court may depart from the guidelines.

(a) The appropriate reduction shall be determined by the court for reasons stated that may include, but are not limited to, consideration of the following:

(1) the court’s evaluation of the significance and usefulness of the defendant’s assistance, taking into consideration the government’s evaluation of the assistance rendered;
(2) the truthfulness, completeness, and reliability of any information or testimony provided by the defendant;
(3) the nature and extent of the defendant’s assistance;
(4) any injury suffered, or any danger or risk of injury to the defendant or his family resulting from his assistance;
(5) the timeliness of the defendant’s assistance.