MEXICO CITY (AP) — Volunteer searchers said they have found a clandestine crematorium on the edge of Mexico City.

It’s the first time in recent memory that anyone claimed to have found such a body disposal site in the capital. In northern Mexico, drug cartels often use drums filled with diesel or caustic substances to burn or dissolve bodies, but up to now there has been little evidence of that in Mexico City.

Ceci Flores, a leader of one of the groups of so-called “searching mothers” from northern Mexico, announced on social media late Tuesday her team had found bones around a charred pit on the outskirts of the city.

Flores said the team had found bones, clandestine burial pits and ID cards at the site in a rural area of the city’s south side.

Mexico City prosecutors issued a statement saying they were investigating the find to determine the nature of the remains found, and whether they were human. The prosecutors office said it was also reviewing security camera footage and looking for possible witnesses.