TIJUANA, Mexico – Mexico's federal attorney general's office says three decapitated bodies were found in an empty lot outside Tijuana.

Officials said the bodies discovered Tuesday had messages on their backs, but would not give details about what the notes said.

Witnesses said the bodies had their hands tied behind their backs. The heads were found nearby and appeared to have been burned.

The killings were the latest in a wave of mostly drug-related violence that has swept Mexico. Cartels have turned to decapitating their victims as a way to intimidate their rivals.

Another decapitated body and a man who had been stabbed to death were found Monday on the outskirts of Tijuana.