MEXICO CITY — Mexico City authorities are running DNA tests to determine the identity and origin of 42 human skulls found at an altar in a drug gang hideout.

The mound of skulls was piled around what appeared to be an altar of an Afro-Caribbean religion.

A raid by hundreds of police on a labyrinthine Mexico City slum complex last week yielded the skulls, two methamphetamine labs, guns, grenades and about 2 ½ tons of marijuana.

Mayor Claudia Sheinbaum said Sunday genetic profiles from the skulls would be compared to lists of missing persons.

It's not clear if the skulls belong to gang victims or were stolen from graveyards. Bones also sometimes emerge because of above-ground burial niches and the tradition of cleaning grave sites for reuse after a few decades.