MEXICO CITY (AP) — Mexican security officials say that what really interested United States authorities in a son of imprisoned drug lord Joaquin "El Chapo" Guzmán last month was his fentanyl business.

Ovidio Guzmán López was indicted in a U.S. federal court on charges of trafficking cocaine, methamphetamine and marijuana. There was no mention in that indictment of the synthetic opioid ravaging U.S. communities.

Mexican Public Safety Secretary Alfonso Durazo said Friday that Guzmán's alleged fentanyl trafficking to the U.S. was one of the main factors in a U.S. extradition request.

Two covert fentanyl labs have been found in the Culiacan area this year, the last one in August.

On Oct. 17, Mexican security forces captured and later released Guzmán in a failed operation. Thirteen people were killed in gun battles around Culiacan.