Four former members of the Colombian army's special forces are training members of Los Zetas, considered Mexico's most violent drug cartel, the Bogota daily El Tiempo reported Sunday. The retired soldiers - two captains and two sergeants - served time in Colombia for human rights violations. "The identities of the soldiers have not been released because charges have not been filed against them," El Tiempo said, adding that the U.S. Drug Enforcement Administration, Mexican police and Colombian police were tracking their movements.