A reputed lieutenant of captured drug lord Joaquin "El Chapo" Guzman has pleaded guilty in a federal courtroom in Chicago to a $1 billion trafficking conspiracy.

Alfredo Vasquez Hernandez entered the plea Tuesday during what was scheduled as a standard pre-trial hearing. The 58-year-old's trial is set for May 12.

The Sinaloa cartel's alleged logistics chief had planned to plead guilty earlier this year. But his attorney said at the time that his client changed his mind out of fear for his family's safety. He cited a Chicago TV report that wrongly suggested Hernandez had turned on Guzman.

Defense attorney Paul Brayman said Tuesday that enough time had passed since the TV report to allay his client's concerns.

An admitted cartel lieutenant, Vicente Zambada, has also pleaded guilty.