The Washington Post said Wednesday the witness told a judicial hearing that Gen. Mario Montoya cooperated with the death squads that terrorized poor neighborhoods in Medellin that were controlled by leftist guerrillas a few years ago.
Montoya has not been charged in connection with the investigation, but an official at the Colombian attorney general's office told the Post "that is the next step."
The Post said the allegations come as a blow to the United States. Montoya has been the overseer of U.S. military aid to Colombia and helped plan the high-profile rescue of four hostages held by the rebels.
Notable deaths of 2014 [PHOTOS]