The rattletrap sedan cruised the streets of Iguala, its roof crowned by a loudspeaker blaring headlines from the day's newspaper: "Another killed! Another killed!"

To the residents of Iguala, however, this hardly seemed like news. Bloodshed was part of life in Iguala before local police allegedly disappeared 43 college students here in September, and it remains so now. Despite federal efforts to wrest control, the 600 federal officers and 1,000 soldiers sent in five months ago to replace the city's police force have had no effects on the killings and kidnappings.

In a week during late February and early March, for example, at least 19 people were killed in this city of 140,000, many struck down in mafia-style hits by gunmen on motorcycles.

The violence continues because Iguala's most lucrative business still thrives: the opium trade. The city sits on a flat plain halfway between Mexico City and Acapulco in the state of Guerrero, surrounded by steep mountains where farmers milk fields of poppies for opium paste. Rural highways radiate out of mountain valleys toward Iguala, funneling the opium through a key crossroad on the journey north to the United States.

According to one federal case in the U.S., heroin dealers on the streets of Chicago have numbers in their cellphones with the Iguala area code.

"Iguala is the route and that hasn't changed, nor will it," said Marina Hernández de la Garza, a city councilwoman. "The bad guys haven't left. They're parked here."

Gangs fight for territory and profits. In the months leading up to the disappearance of the 43, Iguala's ruling cartel, the Guerreros Unidos, worked with police to set up check points to screen for enemies coming into their territory. An untold number of people were pulled out of cars or buses and disappeared.

While no one has been able to tie the disappearance of the 43 directly to the opium, it created the environment of killings and suspicion the students encountered on the night of Sept. 26, as they came to town intending to hijack buses for a rally.

"They had to disappear 43 people for anyone to pay attention to Iguala," said Cesar Miguel Peñaloza Santana, the mayor in neighboring Cocula, where the students were supposedly killed. "If that didn't happen, no one would be talking."

Nearly half of the heroin found in the United States now is produced in Mexico, up from 39 percent in 2008 and nearly equal to the South American heroin that once dominated the U.S. market, according to the DEA's 2014 National Drug Threat Assessment. And much of the Mexican opium that is processed into heroin comes from the state of Guerrero.

The drug trade has helped make Guerrero one of the most violent states in Mexico. In 2014, there were 1,268 murders or 37.3 per 100,000 residents, by far the country's highest rate.

While Guerreros Unidos controls Iguala, the gang is batting off competitors such as the Rojos, which controls territory to the south of Iguala, including the state capital of Chilpancingo. Mexican federal authorities have said that captured Guerreros Unidos members told investigators the attack on the 43 students from a teachers college was ordered because they believed members the Rojos were among the students. Federal investigators say Iguala police officers, acting on the orders of Mayor José Luis Abarca turned the students over to Guerreros Unidos, which killed them and incinerated their bodies.

More than 100 suspects have been detained in the case, including Abarca and his wife, whose family has been linked to the Guerreros Unidos gang. The suspects also include 44 police officers and at least 17 alleged cartel members.

Mexican security expert Jorge Chabat said it will take more than arrests and federal forces to address the drug trafficking problem in Guerrero.

"Without deeper reforms, without ending impunity and reinforcing the rule of law, in spite of the federal presence, nothing much happens," Chabat said. "They capture some, but the networks remain there."

In the weeks before the students' abduction, residents recalled heated battles.

In August, gunmen abruptly closed off a highway linking Iguala and Chilpancingo. When authorities reopened the road hours later, they found some 200 shell casings and a decapitated body.

Iguala's police, loyal to the Guerreros Unidos, often maintained checkpoints at the city's entrances to look for Rojos. Local residents who asked not to be named to protect their safety said police stopped buses and cars and took people away who were not heard from again.

After the students disappeared, relatives and supporters scoured the hills surrounding Iguala and turned up one clandestine grave after another, finding dozens of bodies of other victims of the simmering conflict. Since October, families of 380 people have come forward to register their loved ones as missing.

In addition to the Rojos to the south, Guerreros Unidos has been fighting the La Familia cartel on its western flank. Last month, gunmen abducted 18 people from a commuter bus on the highway between Cocula and Nuevo Balsas, a town controlled by La Familia.

With the increased federal presence, things have become quieter in Cocula, where the army has checkpoints on the highway to the north and south. But Cocula Mayor Penaloza is certain the violence will increase once the federal forces leave. Sitting in his office at city hall, where bullet holes pock an interior wall, Penaloza expects the military eventually will move on to other troubled towns.

"Unfortunately, they do not have enough soldiers to defend the whole country," he said.

The lively nightlife once common to Iguala is no more. By day, city council members travel with body guards and even drug dealers move in groups, circling the main square on motorcycles until a customer flags them down.

Residents have grown accustomed to frequent calls and text messages from family members who insist on receiving word once they are safely at home. One woman confessed that her parents have asked her by phone to turn on her television as proof. Word of a shootout in town sets off a panicked flurry of such exchanges.

Some say the problems started when the mafia entered politics — and politicians joined the mafia.

Before, "they let (the drugs) pass and agreed to leave the people in peace," said one local elected official, who requested anonymity due to safety concerns. "The problem is when the mafia decides to enter politics, because then you can no longer instill any respect or sense of order."

Sofia Mendoza Martínez, an Iguala councilwoman, said there was no dividing line between government leaders and organized crime under Abarca. Her own husband, an agrarian activist, was killed in 2013 after clashing with the now-detained mayor who faces charges in the death.

It's easy for the government to blame it all on organized crime, but often organized crime is taking orders from politicians, said Mendoza, who arrived to an interview with two state police bodyguards. "The federal police are going to leave and we are going to still be here."

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