The severed heads of six state police investigators were found on a public plaza Wednesday in the northern Mexican state of Durango.
The heads were found in the township of Cuencame a day after the officers were reported kidnapped, state prosecutors' spokesman Ruben Lopez said.
There was no information on a possible motive for the slayings, but beheadings are a hallmark of Mexico's brutal drug gang violence. Durango, a mountainous, largely rural state, is a major battleground for drug trafficking territory.
In Tijuana, meanwhile, the bodies of three young men were found in one neighborhood. A fourth body was found outside a hospital and a fifth -- whose hands and feet were bound -- was found dumped near a gas station.
The deaths came a day after 12 bodies were found in Tijuana, including four that had been decapitated and four men who were killed in a shootout at a popular seafood restaurant.
Soldiers arrested six people, including an 18-year-old woman and two teenagers, who allegedly were planning an attack on a pool hall at the same time as the shootout at the restaurant, the military said Wednesday.
The suspects, except for the teenagers, were paraded in front of reporters. Military officials said they were tied to a gang reputedly led by Teodoro Garcia Simental, who authorities say is waging a bloody turf battle with the Arellano Felix cartel in Tijuana.
The city, which sits across the border from San Diego, has seen more than 590 deaths in violence apparently related to drug disputes this year.
In a separate case, police said the dismembered bodies of two men were found in plastic bags Wednesday near the state government's palace in Chilpancingo, the capital of Guerrero, a southwestern state also gripped by gang violence. A message found along with the remains read "Understand kidnappers this is going to keep happening."
Nationwide, more than 14,000 people have died in drug gang violence since President Felipe Calderon sent troops and federal police to fight cartels three years ago.
In Calderon's home state of Michoacan, federal police arrested a leader of La Familia drug cartel suspected in several shooting and grenade attacks on police, including a Dec. 9 shooting that killed one officer.
The suspect, Antonio Chavez Andrade, also known as "the Nephew," told investigators the cartel had stepped up attacks on federal police because crackdowns are hurting La Familia's operational and economic capabilities, according to a statement from the federal Public Safety Secretary.