42 skulls, fetus, 'satanic' altar found from Mexico cartel's den

The den is located in the Tepito neighborhood, a hotbed of illicit commercial activity.

Four skulls were built into the altar. Other skulls were clustered around the altar, that lay in front of a cross with a horned wooden face mask.

Further, authorities found several symbols of a pyramid topped with a hand and a goat's head with a hexagram between its horns.

Overall, at least 42 skulls have been found and authorities are still investigating the origins of the skulls, a spokesperson for the attorney general's office told Reuters.

The spokesperson said that the investigators have found knives, 40 jawbones, the fetus and 30 leg or arm bones at the site.

It wasn't immediately clear if the fetus was a human, the spokesperson added.

Security forces had nabbed the 31 suspects after authorities seized two laboratories which were used to make synthetic drugs, 50 kg of chemical precursors, more than two tons of marijuana and 20 kg of cocaine.

An unspecified amount of money, rocket launchers and grenades were also seized.

However, on Friday, President Andres Manuel Lopez Obrador said that 27 suspects had been released.

Speaking at a press conference, Lopez Obrador said, "Here the important thing is to see what the arguments were that were used to release these people."

He cautioned people against rushing to a judgment saying, "Let's not rush. If someone acted improperly, illegally, if there was corruption, we will condemn it."

The case has been seen as the second high-profile failure of his government.