The scene was straight out of Sam Peckinpah. Late one night this month, Edgar Eusebio Millán Gómez, Mexico's chief of police, returned to his modest flat in the Colonia Guerrero neighbourhood of Mexico City. He chose to live among the poor to stay close to those he was trying to protect from Mexico's rampaging drug lords, whose killing spree this year has left 1,100 corpses in its wake.
Millán's gesture of solidarity was his fatal error. As he flipped on the lights, he was greeted by a barrage of gunfire. An assassin pumped nine bullets into Millán before he was brought to the ground by a bodyguard. As he lay dying, Millán asked his killer who had sent him. The question went unanswered.
Millán's dramatic murder is merely the most daring in a string of assassinations of police chiefs in a war that has been raging in Mexico since President Felipe Calderón turned up the heat on the country's burgeoning drug cartels. The decision to send in 30,000 troops to bolster inadequate and often corrupt local police has led to a number of arrests of leading dealers.
But the strategy has sparked a brutal wave of retaliation against high-ranking policemen. This month, six police chiefs were killed in a single week, police stations have been bombed and police taken hostage; and there have been mass beheadings. At least three police chiefs have applied to the US for asylum.
Mexico is the main artery for smuggling illegal drugs into the US from Latin America. The trade in marijuana, cocaine and methamphetamines is estimated at $23bn a year and the vast profits allow the gangs to buy the latest equipment. While the cartels use corporate jets and submarines to deliver their illicit cargo and are armed with AK-47 assault rifles and bazookas, the Mexican authorities can barely afford to keep their 40-year-old planes in the air.
Awash with cash, the drug lords buy police protection and hire assassins. Millán's death was ordered by Arturo Beltrán Leyva, who had just escaped arrest on Millán's orders. One of those held for Millán's murder is a federal police official working in his office.
Even the arrest of a drug lord is often only a minor setback for the cartels. Soon after Joaquin "Shorty" Guzmán, the most notorious drug baron in the marijuana-producing state of Sinaloa, was taken into custody, he escaped, like Toad of Toad Hall, in a laundry van.
Experts on the drug trade believe Mexico is at a tipping point and could quickly degenerate into widespread lawlessness, just as Colombia did in the Nineties. Ana Maria Salazar, a former US Defense Department official who advised on American military efforts in Colombia, fears the worst.
"The criminal organisations really feel they can get away with murder," she told the Chicago Tribune. "Once the cartels decide to systematically kill cops and there is not going to be any consequences, that's what happened in Colombia." President Bush's response is to ask Congress for up to $1.8bn in aid to Mexico, a gambit that has been poorly received by both right and left.
Some Republicans believe the money would be better spent reinforcing the leaky border with Mexico. Some Democrats, anxious not to offend Latino voters, waver; while Amnesty International opposes giving money to the Mexican military, who have a poor record on human rights.
Nevertheless, last week the House of Representatives approved a $400m grant to provide Mexico with Black Hawk helicopters, faster planes, surveillance equipment and better training for police, prosecutors and judges. It may well be a matter of too little, too late.