MEXICO CITY (Reuters) - Two human heads were discovered in a cooler outside an office of broadcaster Televisa in the Mexican city of Guadalajara, authorities said on Tuesday. It was not clear who the heads belonged to, but the cooler contained a threatening message signed off with  CJNG , the Spanish initials of a drug gang, the Jalisco New Generation Cartel, a security official in the western city said. A second official at the office of the Jalisco state prosecutor said the cooler was left outside an office of the Televisa station.  However, media in the state suggested the gruesome find was directed at an official, not at the broadcaster. Elsewhere in the city, authorities found a second cooler containing a message threatening a judge, and a bag with suspected human remains with another threat, the second official added.  Both officials declined to be identified. In recent years, the CJNG has become one of the most powerful Mexican drug gangs, and authorities blame it for violence that has convulsed much of central and western Mexico. 