Mexican prosecutors are offering 8 million pesos ($658,000) for information leading to the capture of two suspects in the massacre of 72 illegal Central and South American migrants.
Authorities have already arrested eight people in the mass killings last August at a ranch in the northern border state of Tamaulipas.
But the large amount offered for two suspects known by the nicknames "The Coyote" and "The Scorpion" suggests they may have been the ringleaders.
The Attorney General's Office announced the reward Monday along with a separate bounty of 5 million pesos ($411,000) for a third suspect.
Authorities blame the Zetas cartel for the killings. A survivor told police that gunmen shot the migrants after they refused to work for the gang.