Human remains have been discovered stacked in barrels filled with acid in a rural area of Puebla State, Mexico, according to the local prosecutor’s office. The remains appear to belong to at least three people.

The police discovered 10 barrels and nine bags of human remains, which could belong to at least three people, one of them a man in his 50s.

“It’s likely more than three people, we still need to study the contents of the bags,” a Puebla prosecution source told AFP on Saturday. The finding was made on Thursday after an anonymous phone tip, the same source said.

The prosecutor’s office believes the case might be connected with a shooting in Cuautlancingo that broke out in an illegal cockfight den on Tuesday.

At least a hundred hooded men, presumably members of a criminal gang, appeared at the scene, killed two and abducted at least 20 people. Local authorities say they were able to identify at least six suspects, but those who were kidnapped have not been found yet.

One of the most heinous mass kidnappings in Mexico took place on September 26, 2014, when 43 students disappeared near Iguala in Guerrero state. It was later reported that corrupt policemen handed them over to a drug gang. The criminals then reportedly murdered their captives.

Mexicans have staged a number of mass protests since then, demanding justice for the lost students. It was only in 2015 that the authorities arrested one of the gang members, allegedly connected to the students’ abduction and murder.