Reporting from Monterrey, Mexico -- In the seconds before the gunmen burst into the tiny Lozano Garza jewelry store in this city's downtown, three shoppers browsed the display cases.

An unarmed security guard sat by the door.

Then three men with assault rifles ran in, one after the other, the muzzles of their weapons ablaze.

By the time anyone reacted to the gunfire, it was too late. The four people collapsed in the barrage of bullets. One of the gunmen helped another, apparently wounded by a comrade, out of the store. Before the last killer fled, he fired final shots into a customer and the guard.

Twenty-three seconds after they came, the gunmen disappeared into the traffic of busy Francisco Madero Avenue, lined with hardware and lighting shops, taco vendors and newsstands. The page of a catalog on one case fluttered in the breeze.

The killers left the jewelry. Nor did they touch the cash register. They paid no heed to the three video cameras that recorded the entire scene.

Lying dead that afternoon of March 14, 2007, were an off-duty police commander and his wife, Benjamin Espinosa and Griselda Melendez, who apparently were shopping for a religious medallion in gratitude for a successful intestinal operation on their hospitalized infant daughter. Beyond them lay Ignacia Perez, a homemaker who lived on a former garbage dump and sold jewelry to neighbors, who paid her in weekly installments.

Sprawled near the entrance was Fernando Rodriguez, an unarmed security guard who took the $90-a-month job to save for his oldest daughter's 15th birthday celebration. He lived in terror that someone with a gun would come through that door.

A shattered peace

The victims' stories intersected in that jewelry store, but the slaughter recorded on the videotape that day looks to have been rooted in a nearby town that believed itself immune from Mexico's drug war. San Pedro Garza Garcia, southwest of Monterrey, backs up against the Sierra Madre Oriental, 15 miles and a world away from that jewelry store.

It is Latin America's wealthiest town and had long been considered one of its safest. For years, it has been the suburban escape for the industrial dynasties -- the Sada, Garza, Zambrano, Elizondo, Rivero and other families -- that manufactured steel, glass, beer and cement, and turned Monterrey into a global economic player.

Hundreds of sampetrinos, as residents are known, hold Dallas Cowboys season tickets. They shop at Maserati dealerships, and send their children to top-flight private schools. Many can navigate Houston and Aspen better than the barrios where Ignacia Perez, Fernando Rodriguez and police commander Benjamin Espinosa and his wife lived.

When Espinosa was hired as a San Pedro Garza Garcia patrol officer in 1995, it was one of the few good police jobs in Mexico. Officers there were paid about $1,000 a month.

Being a San Pedro police officer "was an honor," said Mauricio Fernandez Garza, San Pedro's mayor from 1989 to 1991. "There was a lot of recognition. They had better uniforms, of higher-quality fabric. There was a lot of training."

Fresh from two years of military service, Espinosa was aggressive and disciplined. Both his jaw and his crew cut were sharp. "He was a police officer 24 hours a day. He was very active," said Camilo Cantu, a former San Pedro chief of police.

Espinosa went to McAllen, Texas, every few months for training and target practice sponsored by U.S. law enforcement.

San Pedro police had a maximum response time of two minutes. That was possible because San Pedro never had much crime. Fernandez Garza remembers no homicides during his tenure, and in a town full of banks, only one bank robbery. No one could remember a San Pedro police officer being killed in the line of duty in those days.

The town elites kept a firm hand.

"When a daughter was marrying someone from outside," said Gilberto Marcos, a businessman and San Pedro community activist, "they'd check his bank accounts . . . to see if his money was made right. We used to look into who these people were, what family they came from. If they didn't check out, you wouldn't speak to them."

But by the late 1990s, San Pedro was being infiltrated by the world its residents had moved there to escape.

Families from Monterrey's middle and upper-middle classes had swelled San Pedro to 120,000 people, triple its size in the 1960s.

The elite's social control ebbed. Among the new residents were out-of-state drug-cartel families who had moved to the one town where their BMWs and bodyguards wouldn't stand out.

In 2001, San Pedro was shocked when resident Felipe de Jesus Mendivil and his wife were arrested after a shootout with police. The federal attorney general's office said police found $7 million and jewelry in 15 suitcases, all believed to have come from drug sales the couple were allegedly laundering for the Juarez drug cartel.

That year, newspapers reported that Benjamin Arellano Felix, head of the Arellano-Felix cartel that controls the flow of drugs from Tijuana, had kept his wife and children in San Pedro for several years.

"We started seeing signs of violence that aren't the usual minor robberies, but rather were kidnappings or executions," said Jose Roberto Mendirichaga, a history professor, civic activist and San Pedro resident.

Members of San Pedro's elite were busy diversifying their once-regional businesses into global companies and navigating Mexico's bumpy democratic transition, said Oscar Flores, a historian.

"They didn't think [drug violence] could come here," Flores said. "By the time they thought all this [drug violence] was important, it had grown a lot."

By 2005, Monterrey, one of Mexico's safest big cities, had become a disputed pathway for drugs headed to the United States.

The Gulf drug cartel controlled the areas of Nuevo Leon state around San Pedro; the city became an island controlled by the Sinaloa cartel, some of whose members had moved there, said a former city official who requested anonymity out of concern for safety.

'These two cartels'

"Many of the problems we're seeing are really between these two cartels," the official said.

Family members of prominent San Pedro businessmen and politicians were kidnapped, among them the brother-in-law of the state director of public safety. Since 2006, five police officers have been killed.

In February 2006, San Pedro Police Chief Hector Ayala was gunned down. That September, Marcelo Garza y Garza, a well-known San Pedro resident and chief of state police investigations, was shot to death outside the town's largest Roman Catholic church.

San Pedro may have paid cops better than the rest of Mexico, but it still paid too little. Several San Pedro SWAT officers left the department and are believed to be working for the cartels.

But Benjamin Espinosa hung in. He rose from street cop to operations commander targeting the city's local drug dealers. His new rank, with a salary of $1,500 a month, afforded his family a telephone but not a car. He often used a city vehicle.

He joined a unit aimed at rooting out corrupt cops. This year he was involved in capturing two supposed cartel gunmen. He was scheduled to take them to a prison near Mexico City on Friday, March 16 of last year. But on the Wednesday before, the 30-year-old went shopping with his wife, also 30, on Francisco Madero Avenue, in the Lozano Garza jewelry store, owned by the family of San Pedro's director of public safety.

Ignacia Perez spent the morning of the day she died sweeping her concrete-block house 15 miles from San Pedro Garza Garcia.

"Nati," as everyone knew her, was a dark, handsome woman, the mother of four boys, and recently a grandmother, at 37.

She lived atop what had been known as Garbage Dump No. 4, at the foot of Cerro del Topo Chico (Small Mole Hill), a mountain that cleaves the northern sections of Monterrey. The city closed the dump and began covering it in the early 1980s, and waves of rural migrants rushed in to grab the land.

At 15, Perez married Jose Luis Rodriguez, a Monterrey garbage man, and the couple squatted on a thoroughfare then taking shape, Avenida Esperanza -- Hope Avenue. They built a shack of pallets, cardboard and plastic tarp, and strung copper cable to a nearby transformer for electricity.

In that shack, Perez grew into a woman and bore their sons. Over several years, her husband built two rooms, eventually adding three others and painting it all light blue.

Years later, the city paved the streets, installed electrical lines and meters, and issued land titles. The spider web of copper cables came down. The once-squatted shantytown entered the new century a working-class neighborhood with most of the essentials.

City services, it's true, remained a rare sight. Yet crime was relatively low. Killings, shootings, kidnappings were things that happened elsewhere.

Through these years, Perez raised her sons. Her husband drank heavily, and she made do with the little money he gave her each week.

Perez's two older sons became garbage men, got married and moved.

"She was a nice mother, though she would scold us at times," said her third son, Victor Rodriguez, 19. "She'd listen to music while she swept and mopped the floors."

Five years ago, Perez began selling jewelry door to door for the Lozano Garza store. She offered rings, earrings, necklaces and bracelets -- all gold-plated, and nothing for more than $40.

She would go down to the store and pick up a few pieces at a time. It was the farthest she traveled from her neighborhood.

After cleaning the house that day, that's where Perez headed. She left money for the telephone, water and electricity bills on the kitchen table. Her sons found it when they returned that afternoon; she'd never done that before.

About noon, she boarded a bus that took her past lines of concrete-block houses like her own and into downtown Monterrey, where she got off at a stop across the street from the jewelry store.

By that time, Fernando Rodriguez had been at his post inside the store for more than four hours.

It was a dull job. Rodriguez would go outside occasionally to talk with Fernando Lizcano, who owned the cellphone shop next door.

"We'd talk about work, the family, sports," Lizcano said. "He'd come from time to time and ask to use the phone."

Rodriguez, from a large rural family, had little education and few skills. At 44, his options were considerably reduced. Most companies didn't hire men his age, except as security guards.

Thus he had struggled to provide his family with a rented house on an unpaved street a mile north of where Perez lived, just west of Esperanza Avenue.

But he remained a cheerful person, untempted by drink or violence. He was a teddy bear of a man who drew joy from his wife, Oralia, and daughters, Esmeralda, Areli and Fernanda, then ages 14, 10 and 3.

Sunday, his only day off, he would take them to parks around Monterrey. The family frequently took photographs.

"Their whole life is in their photos," said Oralia's mother, Angelica Aleman.

He sang often and loved dancing with Oralia. His mother-in-law thought of him as her son.

As a younger man, Rodriguez sold kitchenware door to door. He was a messenger for several years, until he broke his leg in an accident. Then he was hired to clean and guard a beauty school downtown for $80 a week. He learned to clean the school's clippers and machinery. His only fear was that he would have to eject some rowdy customer.

Rodriguez spoke constantly of his wife and daughters and worried how they would manage without him. "They were his world," said Myrna de Luna, owner of the beauty school. "He'd register them for school. He'd shop for his daughters and wife -- buy their dresses, even their underwear."

His main worry was saving for his oldest daughter's quinceañera that July. He wanted a dance hall with a big sound system and many guests.

A few months before the deadly attack, he'd quit the beauty school to work at the jewelry store because it paid $10 a week more, but he never liked the new job. Unarmed and alone, he worried about having to protect the store.

On Saturdays he cleaned the machines at the beauty school for extra cash. "He was looking for money anywhere he could find it," De Luna said. Most other days, he dropped by there to ask for his job back.

To work at the jewelry store, Rodriguez had to leave home early and come back late. The morning before he left for the last time, Oralia asked her husband whether she could look for work. Rodriguez had always said no. But that morning, he said maybe she should, after all, interview for a job.

She went to a factory that day. She was being interviewed in the afternoon when her family sent word that she was needed at home.

The war moves on

On the evening of March 14, Nati Perez's family gathered on Esperanza Avenue, hoping. The shootings had been reported on television and radio. A cousin who worked at the hospital where the city morgue is located called, saying that one of the bodies looked like Nati.

Perez's son Victor and his aunt went to the hospital to see for themselves. "Her face was destroyed, but she had a mole above her lip and that's how my aunt recognized her," Victor recalled.

Monterrey officials pledged to help with the funeral. "It was just promises," Victor said. The family buried her in the city cemetery near the state prison.

Abraham, her youngest son, seldom ate; her husband spent his nights crying in the upstairs bedroom he had built for the couple. He has stopped drinking. Perez's sister drops by to cook and clean the house on Esperanza Avenue.

"It doesn't feel the same," said nephew Joel Lopez. "Here my aunt was everything. She was the one who gave the house spirit."

Merchants along Francisco Madero Avenue say they miss Fernando Rodriguez.

"It took a long time to get used to the idea that he was dead," said Lizcano, who ran from his cellphone shop after the shooting and was the first to find the bodies.

For his daughter's 15th birthday last year, the Rodriguez family held a modest dinner at their house.

The jewelry store moved two days after the attack. The storefront that housed it is the only unrented space for blocks.

The four killings remain unexplained. The families have heard nothing from officials. The video shows no clerks or manager in the store at the time of the shooting -- a source said the staff was upstairs eating lunch.

One theory is that the killers ambushed Espinosa to send a message to San Pedro's director of public safety, Rogelio Lozano, whose family owns a chain of jewelry stores that included the shop attacked.

"The citizens have to guess," said Marcos, the businessman and San Pedro community activist. "One guess is that [Espinosa] was involved with one gang and the other killed him. Or there's the one that you'd like to believe, which is that, for having done his job, they killed him."

Kidnappings of important sampetrinos continue. In August, 17 months after the slayings, thousands of residents marched through the streets of downtown Monterrey as part of a national mobilization against drug violence. The cartels' warring, meanwhile, has drifted elsewhere; it has left more than 6,000 fatalities nationwide in less than two years.

But in San Pedro, the killing of Espinosa created little sustained outrage. There were no fundraisers, no trusts set up for his daughters.

The girls live with their mother's family. Their grandfather, Lucio Melendez, 57, supports them. He earns $100 a week as a security guard, and wonders why anyone in Mexico would want to be a cop.

Quinones is a Times staff writer.

sam.quinones@latimes.com

latimes.com /siege

About this series

A team of Los Angeles Times reporters and photographers has been chronicling drug-related violence that has claimed more than 6,000 lives in Mexico in less than two years. Earlier stories and additional material, including the security-camera footage of the slayings described in this story, are available online.