Mexico ? Police in Cancun found 12 decomposing bodies in four caverns and were searching for more cadavers in violence blamed on drug gangs in the popular resort city, officials said Friday.

Earlier this month, police discovered six other bodies in a similar cavern near the Mexican resort. Three of the bodies had the letter “Z” carved on their abdomens — a possible reference to the Zeta drug gang.

Police say detained gunmen have led them to all the clandestine graves — dried up sinkhole caves, known as cenotes.