Mexico is trying to break the influence of the powerful cartel
By Stephen Gibbs
BBC News, Mexico City
They decapitate, torture, and extort. Then they pray, and donate to charity.
The "Familia" cartel is perhaps the most extreme example of the paradoxical enemy which Mexico faces as it tries to defeat organised crime.
It is a fight which would be much easier if the cartels were simply maverick gangs on the fringe of society.
But they are, in many areas, part of society.
"La Familia was originally a social structure. And in many ways it still is," says a former Mexico deputy attorney general and organised crime expert, Prof Samuel Gonzalez Ruiz.
The group is believed to have originated in the 1980s as a loose self-protecting coalition between marijuana and opium farmers in the state of Michoacan.
By the 1990s the farmers, who had formed an alliance with the neighbouring Gulf cartel, were running a profitable smuggling business.
Like other Mexican drug cartels, they were benefitting from the massive, successful, clampdown on drug trafficking led by the US authorities across the Caribbean. The strategy pushed the flow of drugs west, into Mexican territory.
La Familia found itself in control of key entry points for cocaine on Mexico's Pacific coast.
La Familia is blamed for many attacks and murders in Michaocan
The leaders of the organisation did not waste the opportunity. They embarked on a major expansion and diversification programme.
They invested in the production of the synthetic drug methamphetamine in the state. They took over the local pirate DVD business, and set up a brutal debt collection service.
Research by Prof Gonzalez's team suggests that 85% of the legitimate businesses in Michoacan now have some link with La Familia, or with its money.
Income from the group is understood to have funded schools, drainage projects, even churches.
One curious feature of the organisation is that, according to Mexican intelligence documents, it strongly discourages its members from consuming alcohol or drugs, and has a quasi-religious ideology.
The group's alleged spiritual leader, Nazario Moreno Gonzalez, also known as "El Mas Loco", or "the maddest one" is understood to have published and distributed his own bible, based on the macho Christian writing of contemporary American author John Eldredge.
"It is clearly an organisational tool," says anthropologist and analyst Dr Elio Masferrer, of the group's religious faith.
"It does not matter whether or not the leaders believe in it".
Notes, signed by La Familia, are often left on the mutilated bodies of their rivals, indicating that they are victims of "divine justice".
Thousands of soldiers have been deployed to tackle the violence
The last three years have seen increasingly bold attempts by the cartel to intimidate its enemies.
In 2006, five severed heads were thrown into a night club in the town of Uruapan. A letter accompanying the heads declared: "only those who deserve to die will die."
In 2008, a grenade was thrown into a crowd celebrating Independence Day in Morelia, the state capital. And earlier this year, in apparent revenge for the arrest of one of the cartel's leaders, 12 federal police officers were captured, tortured and murdered.
That prompted an all-out assault by the Mexican government. President Felipe Calderon despatched thousands of additional troops and police to Michoacan, which happens to be his home state.
The government also says it has evidence that La Familia has been using its economic power to buy political power.
In May, federal authorities arrested 10 mayors and 20 other local officials in Michoacan, alleging they had sold favours to La Familia.
The latest arrests in the United States confirm what Mexico has long been warning the US authorities: that the drugs which pour across the border every day bring organised crime with them.
But some believe that particular weaknesses within Mexico have made it especially vulnerable to cartels.
Pervasive unemployment, corruption within law enforcement and huge divisions between rich and poor are the perfect territory in which groups like La Familia can flourish.
"Drug trafficking," says Prof Gonzalez, "is a symptom of a far deeper sickness in this country".