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 and discovered several scorched spots in a nearby clearing.

A Public Safety Department statement sent late Sunday said police suspect the heads were burned in the clearing, though it did not say what evidence they 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, many of whom believe that the "saint" — not recognized by the Roman Catholic Church — can keep them from getting caught or killed. Many people not engaged in criminal activities also worship the Santa Muerte in hopes of gaining favors or intercession.

Rituals performed for the Santa Muerte include offerings of cigarettes, candy and prayers based on a modified version of catholic rites, but do not normally include any kind of 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.