When soldiers tried to halt a suspicious-looking SUV that was being escorted through Monterrey by a state policeman, the officer radioed for backup. In minutes, police from 40 patrol cars surrounded the troops, drawing their guns and sending the soldiers diving for cover in an hour-long standoff.
Confrontations like that are happening with increasing frequency in Mexico's wealthiest city as soldiers fight corrupt police officers helping drug cartels _ in addition to taking on the drug dealers themselves.
This year alone, police and soldiers have confronted one another more than 65 times, The Associated Press has learned _ a growing and dangerous trend in the war on drugs.
Things are so bad, the general in charge of army operations in northeastern Mexico told the AP, that he has warned police chiefs his men are ready to open fire on police if it happens again.
"The moment they shoot at us, get in our way, use their guns to protect criminals, they become criminals themselves," said Gen. Guillermo Moreno, who commands troops in Nuevo Leon and Tamaulipas states along the Texas border.
President Felipe Calderon has acknowledged that corruption permeates Mexico's low-paid police at all levels and therefore has opted to combat the billion-dollar drug-smuggling industry by relying primarily on the military, which has seen remarkably fewer cases of bribery by traffickers. His administration also has sent in federal police and soldiers, both of whom are higher paid and usually better educated, to go after police on the take.
As a result, distrust between police and soldiers runs high. But nowhere has it exploded like in Monterrey, an industrial hub two hours from Laredo, Texas.
That point was driven home Wednesday with the brazen killing of army Brig. Gen. Juan Arturo Esparza shortly after he was named police chief in the suburb of Garcia. Five Garcia police were among 10 people arrested in the case Thursday.
Most of the problem comes from the fact that Nuevo Leon has not purged corrupt police from its ranks like other states have.
The police chief of Ciudad Juarez _ a retired army general _ has fired hundreds of officers suspected of corruption in the past year, and the army trains new recruits, many of whom are former soldiers. In western Michoacan state, home to the violent La Familia cartel, state police take regular drug tests and have their guns checked every six months to ensure they have not been used in crimes.
Army generals in charge of each region decide whether to invite state police to work with them, and most have done so. But Moreno said he doesn't trust Nuevo Leon police.
"For the safety of our troops and their families, we carry out our operations by ourselves," he said.
The confrontations have jumped from two in 2008 to 67 this year, Moreno said. They range from soldiers stopping officers who were following them to spy for drug cartels, to exchanges of gunfire with police guarding drug lords. In one incident, a police officer was shot in the leg.
The Oct. 13 standoff involving the soldiers and police from 40 patrol cars ended peacefully, but not before some tense moments captured on video by a TV crew.
The dozens of police who responded to the officer's call for backup lined up to take aim at the troops, who pointed back with high-powered rifles.
Army and police commanders talked face-to-face and ordered their men to stand down. The men obeyed _ but not without some resentment.
"We're all in this together, and we should support each other," a police commander is heard telling one of the soldiers on the video.
"No, we're not," the soldier snaps back. "We have arrested many police officers who are not in this with us."
More than 100 Monterrey police officers have been detained this year on suspicion of links to organized crime. Soldiers have found officers referenced in lists seized from drug traffickers detailing who was receiving bribes.
Many police are suspected of working for the Zetas, a group of former army soldiers-turned-enforcers for the cartel known for its meticulous record-keeping as much as its brutal tactics.
Those arrested include two Nuevo Leon state officers accused of taking part in the abduction of nine soldiers allegedly in retaliation for the army's anti-drug operations.
Officials recently detained two other officers from the same force on suspicion of kidnapping two army lieutenants who were moonlighting as bodyguards for a lawyer. They have not been seen since Sept. 25.
"We believe a significant percentage of these officers have links to organized crime, either by collusion or because they were intimidated and are afraid," Moreno said.
Acting on his recommendations, state authorities in June banned officers from using cell phones during work hours to try to prevent them from tipping off criminals to raids by soldiers and federal agents. They also stripped most state and city police officers of their automatic rifles _ to protect troops.
Esparza's slaying four days after his appointment was the third time a military officer hired to professionalize a city police force in Mexico has been killed this year.
More than three dozen gunmen in about 10 SUVs ambushed and killed Esparza. Two former soldiers and two Garcia police officers accompanying him also were killed.
Monterrey Mayor Fernando Larrazabal has ordered the city's 1,000 traffic officers off the streets while his administration makes sure they are clean. He said officers will undergo polygraph tests, and a new citizen-run council will investigate police corruption.
The state's new security secretary, Carlos Jauregui, did not respond to an AP request to detail his plan.
Mexico's top federal cop, Public Safety Secretary Genaro Garcia Luna, says the only way to resolve the problem is to get rid of the low-paid city police forces, many of which have seen little improvement after being purged repeatedly in the past decade.
He wants to create state law enforcement agencies to oversee Mexico's 31 states and the federal district of Mexico City. The government would raise officers' salaries significantly to deter bribery.
Garcia Luna presented his ideas to state police chiefs who met last week to discuss a report on police that calls city police "an easy target for corruption." It said more than 60 percent of the 159,734 city police receive monthly salaries of only 4,000 pesos (about $300). Most have less than 10 years' education, and many are illiterate.
Incorporating them into state forces would help prevent organized crime from corrupting them, the report said.
"In Mexico, infiltration by organized crime among local police ranks is very widespread," said Martin Barron, a national security specialist at the National Institute of Criminal Justice, a government think-tank. "Police are so low paid that unfortunately they have to make up for that, and they do so through corruption _ either by asking for bribes from citizens, passing information to the cartels, turning their heads or doing other things for the gangs."
U.S. anti-drug officials have long complained that corruption among Mexican police has hindered cross-border efforts to fight drug cartels. But they say Mexico has made great strides to clean up forces, especially on the federal level, and the two nations' law enforcement are working closer than ever before.
Nevertheless, Mexican federal officers, like soldiers, often find themselves working in areas surrounded by state and local police on the take.
Police concede that corruption in their forces has helped the cartels build deep criminal networks across Mexico. But they seethe at the condescending attitude of more than 45,000 troops sent to drug hot spots. Police say soldiers often treat them as if they are all corrupt.
"It's humiliating," said Jorge Castaneda, a 23-year veteran of the Monterrey police. "They pull you from your patrol car. They take away your cell phone, if you have one, and they even take your gun. We're here because we want to wear this uniform, but people don't appreciate our work."
Associated Press writer Mark Walsh contributed to this report.