MEXICO CITY – The heads of 11 decapitated bodies discovered in Mexico's Yucatan Peninsula last week may have been burned in a ritual, investigators said.

Police said they found an altar to the skeletal figure of the “Santa Muerte,” an unofficial patron saint of death, in the home of two men arrested in connection with the slayings, while several scorched spots were discovered in a nearby clearing.

Police suspect the heads were burned in the clearing, according to a statement from the Public Safety Department. The department did not say what evidence it had to support that theory. Public Safety officials declined to give further details Monday, citing an ongoing investigation.

Decapitations have become more frequent in battles between Mexico's powerful drug cartels. The 11 corpses appeared to be the largest group of beheadings since gunmen tossed five human heads into a bar two years ago.

The bodies were found piled on top of each other Thursday in a field outside Merida, a city in the Yucatan Peninsula that had largely been spared from drug violence.

The next day, police arrested three suspects with a bloody hatchet and other weapons after a shootout and a highway chase. Police say they acknowledged belonging to the Zetas, a group of hit men tied to the Gulf cartel. The suspects have not yet been charged.

The Santa Muerte is one of several unofficial folk saints worshipped in Mexico. The cult has become popular among criminals in Mexico who appeal to the “saint” – not recognized by the Roman Catholic Church – to stay safe and out of jail. Law-abiding worshippers simply seek favors or intercession.

But Santa Muerte rituals normally do not include blood sacrifice.

If police suspicions about the ritual burning prove true, it would recall the 1989 killing of a Texas college student and 12 other people by a drug trafficking cult.

Student Mark Kilroy's mutilated body was unearthed a month after the 21-year-old vanished while on spring break in Matamoros, a border town across from Brownsville, Texas. The cult believed human sacrifice would protect it from police and rivals. Its high priestess and four of her followers were sentenced to more than 60 years in prison in 1994.

Mexicans are increasingly angry about rising violence, and on Saturday well over 100,000 people marched in cities nationwide to demand the government put an end to daily killings, kidnappings and shootouts.