Mexico City  - They led the federal police officers into an ambush, killed them systematically with a single shot in the neck and dumped the bodies alongside the road in Mexico's western state of Michoacan.

As if the message from the drug cartel hadn't been loud enough, the killers left something else alongside the bodies of the 11 men and one woman who had been investigating the drug trade in the state: a written note threatening further violence against police, according to Mexico's National Security Council.

The council's spokesman Monte Alejandro Rubido, who spoke to reporters in Mexico City Tuesday, placed the blame for the murder of the federal officers on the relatively young drug cartel, La Familia Michoacana, which has its stronghold in Michoacan state.

Officials said the latest round of blood letting was triggered by the arrest Saturday of the boss of La Familia's killer squadron Arnoldo Rueda Medina, also a top drug trafficking suspect. Photographs show a handcuffed Medina being led off by two heavily- armed police officers wearing masks for their own personal security.

Not a shot was fired when Rueda Medina was arrested as he arrived at his home in Michoacan capital Morelia, but La Familia attempted to free him through a subsequent series of attacks against a score of police facilities that took at least five lives and injured many more.

Officials said the attackers may have also been prepared to kill Medina if they couldn't free him, in order to prevent him from talking to police.

La Familia was hardly on anyone's radar three years ago. But since they made their horrific debut in late 2006, they have steadily forged a tyrannical image in the drug wars of Mexico, where drug- related violence claimed 6,290 lives in 2008, and over 3,000 so far this year.

Until 2006, the monopoly on drug terror belonged to the traditionally infamous cartels of Sinaloa, the Gulf with its armed wing Los Zetas, Juarez and Tijuana.

But in the early hours of September 6, 2006, La Familia burst onto the scene when armed masked attackers stampeded into the Sol y Sombra bar in Uruapan, Michoacan and bowled five bloody human heads onto the dance floor with a message.

"La Familia will not kill for money, it will not kill women, it will not kill innocent people, it will only kill those who must die. Let all people know that, this is divine justice," the text said.

After conquering the Michoacan scene, La Familia has expanded its fight to other states in western, southern and central Mexico, taking on its old allies Los Zetas for control of the drug trade and other businesses like extortion and kidnappings.

Although the history is murky, La Familia was apparently formed with the backing of Los Zetas which hoped to use the new arrivals to block the Sinaloa drug cartel from expanding. The liaison disintegrated in 2008 into a bitter rivalry.

La Familia's leaders are Nazario Moreno, alias "El Chayo," and Servando Gomez, alias "El Chango Mendez."

Seeking to create an image of a Robin-Hood-like advocate for the poor and the innocent, the leaders use religious references when they talk about themselves, according to documents seized by the authorities.

Mexican President Felipe Calderon, who took office three months after the head bowling incident, has a special interest in La Familia, as they operate in his native state. That helps to explain why Calderon chose Michoacan to launch a serious federal war on drugs and drug violence that has gradually expanded to much of Mexico.

In one of their responses to Calderon's campaign, a cartel carried out a shocking mass attack on civilians last September in the president's very own back yard in the state capital of Morelia - the first mass attack of its kind in Mexico's drug wars.

Charging into the packed crowd on Mexican Independence Day, the cartel killed eight people and injured another 100.

La Familia distanced itself from the attack and blamed Los Zetas. Following a tip about the alleged culprits, federal forces showed up at a house to find three alleged Zetas members beaten up and handcuffed.

On Tuesday, the Mexican daily Reforma described the cartel's extortion-based fundraising system in Michoacan that uses informers inside public institutions, expropriates land for drug cultivation and commandeers vehicles from the police pound to carry out crimes.

Before taking office in 2007, Michoacan Governor Leonel Godoy told the newspaper he was warned by the Army that La Familia had summoned 89 mayors-elect to a meeting. A total of 28 mayors actually showed up at the gathering.

Eight mayors and about 20 state officials - including the state attorney general - have been under arrest for two months for allegedly providing La Familia with protection.

The cartel's two bosses are among Mexico's 24 most wanted drug lords, and the Justice Ministry is offering a reward of 2.2 million dollars for each of them. (dpa)