The Mexican army has arrested suspects over the slaughter of 49 people who were decapitated, mutilated and left in plastic bags on the side of a highway.
Among those arrested was Daniel Elizondo, known as "El Loco" ("the crazy man") and believed to be the leader of the gang that carried out the killings, an official in the Nuevo Leon prosecutor's office in northern Mexico said on Saturday.
The corpses, whose hands had been cut off to prevent fingerprint identification, were discovered a week ago close to the northern city of Monterrey.
The incident is among the largest and most gruesome massacres attributed to the scourge of drug trafficking in Mexico, itself blamed for about 50,000 deaths since December 2006.
A note was found at the scene in which the Zetas claimed responsibility. But in recent days, poster ads attributed to the gang have denied responsibility, accusing their former allies from the Gulf cartel instead.
A day earlier, the army said it had detained a retired officer over alleged links to drug cartels, bringing the number of high-ranking officers detained in recent weeks to four.
One of the men arrested earlier this month is General Tomas Angeles Dauahare, who President Felipe Calderon named as assistant defence secretary in 2006. He left the post in 2008, when he retired.
An official at the attorney general's office said Dauahare and another of the officers are suspected of protecting members of the Beltran Leyva cartel in a case dating back to 2009.
The leader of the cartel, Arturo Beltran Leyva, was killed in a shootout with Mexican marines at an apartment complex in Cuernavaca in 2009. The marines were reportedly called in to look for the capo after the army appeared to be slow to act on US intelligence indicating the drug lord's location, according to a leaked US embassy diplomatic cable from late 2009.
Angeles Dauahare's lawyer, Alejandro Ortega, said on Thursday that he has not been allowed to talk to his client, but he said the general told his wife he is being accused of taking money from associates of an alleged hit man for Beltran Leyva.
In another development related to the drug violence, the tortured body of a crime reporter was found on the side of a road in the northern state of Sonora on Friday, a day after he was kidnapped by gunmen while waiting at a car wash, authorities said.
Marco Antonio Avila Garcia's body was found inside a black plastic bag near the city of Empalme, the Sonora state prosecutors' spokesman Jose Larrinaga said.
Eduardo Flores, director of the sister newspapers Diario Sonora de la Tarde and El Regional of Ciudad Obregon which the reporter wrote for, told The Associated Press news agency that Avila wrote about drug trafficking but never mentioned cartels by name nor did investigative pieces.
"He wrote about drug trafficking, but nothing involved" about it, Flores said. "He wasn't allowed to cover anything that would be considered aggressive by criminal groups."