MONTERREY, Mexico (AP) — Lorena Villareal Elizondo went to meet a friend at the Casino Royale, a popular low-cost lunch spot, when armed men burst through the door shouting: “Get out! Get out! We’re going to burn everything!”

It was only 19-year-old Carla Maria Espinoza Vega‘s second day at work at the casino when the intruders sprinkled accelerant around the front door and set the building on fire.

Friends and family mourned Villareal, a 39-year-old mother of three, at a visitation Friday, while Espinoza’s mother filled out paperwork to retrieve her body.

Mexicans have endured plenty of horrific crimes during their country‘s bloody five-year war against drug gangs. But the arson in the northern Mexican city that killed 52, mostly women, was a macabre milestone in a conflict that’s claimed more than 35,000 people since 2006, according to government figures. Others put the toll near 40,000.

The victims this time weren‘t cartel foot soldiers or migrants resisting forced recruitment by gangs, as were the cases in other attacks. They were workers or customers who liked to lunch or play bingo and slots in the afternoons in an affluent part of town.

“She was my baby,” said Espinoza’s tearful mother, Guadalupe Vega, as she waited at the morgue.

“She was like my sister,” said Villareal‘s cousin, Guadalupe Elizondo Gracia, outside a giant funeral home that drew hundreds of mourners to a half-dozen visitations Friday night.

In a nationally televised speech, an angry President Felipe Calderon declared three days of mourning and labeled the attack the worst against civilians in the nation’s recent history.

“We are facing true terrorists who have gone beyond all limits,” said Calderon, who also announced he is sending more federal forces to the city of 1 million people. “Today, Mexico is upset and saddened and we have to transform this sadness and this grief into courage and valor to face ... these criminals.”

Hours later, he appeared in front of the burned-out casino and place a large wreath and observe of moment of silence.

A surveillance tape released Friday showed eight or nine men arriving in four cars and carrying canisters into the building, which was engulfed in flames in little more than two minutes as people tried to flee in panic.

Calderon offered a $2.4 million reward for information leading to their capture, the same amount offered for the arrest of top drug lords. Authorities had sketches of three of the men based on interviews with 16 survivors of the fire, said Jorge Domene, Nuevo Leon state security spokesman.

He also said officials had located three of the four vehicles in the video, dumped around various parts of the city. All had been reported stolen.

Authorities said they are still investigating whether the exits were blocked. But many bodies were found in offices and the bathrooms, indicating they were expecting a shootout.

“They sought places to protect themselves from firearms,” said Jorge Camacho Rincon, civil protection director for the state of Nuevo Leon. “They went running to closed areas.”

Most died of smoke inhalation and were found clutching cell phones in their hands, a law-enforcement official who wasn‘t authorized to be quoted by name told The Associated Press.

In the streets around the casino on Friday, people said the latest violence deepened their sense of vulnerability. In recent years, the city has been ensnared in a turf battle between the Gulf cartel and its offshoot, the Zetas, and is on track for record levels of killings this year.

The casino was attacked twice before. In May, gunmen strafed it from the outside. Last month, gunmen killed 20 people at a bar.

“What happened last night was the limit,” said a man nursing a Coke at a hamburger stand across from the city’s morgue, where families streamed in all night to identify bodies. Like many people, he refused to give his name out of fear.

“We don‘t know how to protect ourselves or whom we’re talking to,” he said. “We don‘t have security right now.”

The attack resonated across the country because many of the victims were from the middle class, so far mostly untouched by violence, said Jorge Chabat, an expert in safety and drug trafficking at the Center for Research and Teaching in Economics.

“We’re talking about an attack on a civilian population of a certain income,” he said. “Because who was there was from the middle class, the upper middle class of an important city in Mexico.”

Villareal, who had a travel agency near the casino, intended to meet a friend for lunch, but the person had just left by the time she arrived, said Francisco Medina, 41, a close friend and neighbor who also came to the visitation packed with people and giant flower wreaths.

“She decided to stay and eat alone when the bad luck came,” he said.