Fifty-nine bodies were found buried in pits in the state of Tamaulipas in northern Mexico, near the site where suspected drug gang members massacred 72 migrants last summer.
Security forces stumbled on the site as they were investigating reports that passengers had been forced off buses by gunmen in the area in an apparent attempt at forced recruitment by a drug gang.
State and federal authorities conducted a raid, detaining several suspected kidnappers and rescuing five kidnap victims.
Then they made a grisly discovery – eight pits, containing 59 corpses. One of the pits held 43 dead.
Tamaulipas state interior secretary Morelos Canseco said two of the dead were women. Many of the victims found in the pits appeared to have died between 10 and 15 days ago, dates that would roughly match the bus abductions, he said.
Mr Canseco said state officials began getting reports that gunmen had been stopping buses, from about 25 March.
At least two more cases were reported in the following days. The buses were allowed to continue on with their remaining passengers.
The bodies were being examined to determine their identities and the causes of death, the Tamaulipas state government said in statement in which it "energetically condemned" the crimes.