Medical examiners, in plastic boots, performed a dozen autopsies a day as families of victims waited outside in numbers sufficient to require a line.

For all this, Mexico has not made much sense of one of the most sensational killing sprees in recent history, which has left 10,500 dead in the streets of Juarez as two powerful drug and crime mafias went to war. In 2010, the peak, there were at least 3,115 aggravated homicides, with many months posting more than 300 deaths, according to the newspaper El Diario.

But the fever seems to have broken.

In July, there were just 48 homicides — 33 by gun, seven by beatings, six by strangulation and two by knife. Of these, 40 are considered by authorities to be related to the drug trade or criminal rivalries.

Authorities attribute the decrease in homicides to their own efforts — patrols by the army, arrests by police, new schools to keep young men out of gangs and in the classroom.

Yet ordinary Mexicans suspect there is another, more credible reason for the decrease in extreme violence: The most-wanted drug lord in the world, Joaquin “El Chapo” Guzman, and his Sinaloa cartel have won control of the local drug trade and smuggling routes north.

From the beginning, Ciudad Juarez has been a key battleground in President Felipe Calderon’s U.S.-backed drug war. It was here that Calderon poured 8,000 troops and police, and millions of dollars in aid, in a surge that his security experts compared to the one in Iraq.

As part of the $1.6 billion Merida Initiative, the U.S. government paid for police academies here, including training for overwhelmed cops in “street survival” skills. The United States provided microscopes to the forensic lab, sent Juarez leaders to Colombia to learn how that country fought violence, helped create an anonymous tip line, and supported programs for at-risk youth.

Calderon says that homicides across Mexico are decreasing, but since his government refuses to release the data, suspicions linger.

Juarez itself is still vulnerable. It has not escaped attention that violence began to recede after soldiers and federal police began to leave the city. Residents pray that the relative peace is maintained, while thousands of families who fled to Texas to escape the violence wonder whether it is safe to return.

At its most ferocious, when this industrial border city on the Rio Grande seemed consumed by a homicidal mania, the murder rate averaged almost nine per day.

Last month, homicides averaged 1.3 a day, the lowest rate since an internecine drug war between the Sinaloa and Juarez drug cartels exploded here in 2007.

“It is a completely different ballgame now,” said Hector Murguía, the mayor. “Our city is no longer a town of ghosts.”

Families have begun to celebrate birthdays in restaurants again. At night, a few customers wander into the downtown cantinas, once a no-go zone after dark. The recession is over, and the assembly plants, which pay about $13 a day, are humming. Some 20,000 jobs have been created, according to city hall.

To respond to the crisis that brought Juarez to the brink, the federal government built schools in poor barrios where they were none, and community centers, playgrounds, clinics. They’ve provided education scholarships and health insurance and given money and materiel — new pickups, bigger guns — to the municipal police, who a few years ago were not just employees of the criminal organizations but the management.

Mexico’s interior secretary, Alejandro Poire, was recently in the city to tout Calderon’s achievements — a 50 percent reduction in the homicide rate here compared with the same period last year and 70 percent from 2010.

“Thanks to the cooperation between federal, state and local governments, as well as public support, we are mending the social fabric,” Poire said.

Critics of government strategy in Juarez, however, point out that the former governor of the state of Chihuahua, which includes Juarez, was himself named as a target of a federal investigation for alleged ties to organized crime, according to media accounts.

A war for control

Though often portrayed as a battle over lucrative drug smuggling routes into the United States, law enforcement officials say the fight between the Sinaloa and Juarez cartels was less about feeding America’s voracious appetite for drugs, and more about control of Juarez.

“From my perspective, the violence had its origin in the sale and consumption of drugs here in Ciudad Juarez; that’s what caused the bulk of the crisis,” said Cesar Peniche, the top federal prosecutor here.

By some estimates, there were thousands of drug distribution points and as many shooting galleries operating in Juarez when the cartels went to war.

Some experts speculate that as it became more difficult to smuggle drugs into the United States, the mafias began paying people in product, which might have increased consumption in Juarez, where a dose of heroin sells for less than $5, the cheapest in North America.

As the federal prosecutor describes it, the cartels unleashed their armies to seize the city. At the top were leaders, such as Guzman, who probably never set foot in Juarez. The actual combatants were a handful of paramilitary-style hit squads, which included former and current police, and thousands of street criminals, lookouts, dope dealers and their customers, as well as impoverished teenage dropouts who were loaned a gun for a few hours.

After thousands of deaths and arrests, Mexican law enforcement officials say Guzman’s enemy, the Juarez cartel, is now a shadow of its former self. A Mexican military commander said the Juarez cartel is having trouble paying its members. A Mexican state prosecutor said the Juarez organization has run out of recruits, weapons, vehicles and money.

Officials in the Drug Enforcement Administration say both cartels were wounded in the fight but that Guzman’s organization emerged on top.

Stoking the violence were two hyper-violent gangs called the Artistic Assassins and the Aztecas and two local leaders who pursued a strategy of mutual extermination until their capture last year.

Jose “El Diego” Acosta of the Juarez cartel was caught with intelligence from the DEA. He allegedly ordered the execution of 19 drug addicts at a halfway house. His counterpart for Sinaloa was Noel “El Flaco” Salgueiro, arrested by the military and blamed for the torture-killing of the brother of the state attorney general, whose “confession” was put up on YouTube.

Making matters worse, municipal police officers formed a crime collective known as the Line, and worked for the Juarez cartel. A third of the local police was fired or quit for ties to criminal organizations in 2008, the first of many ongoing attempts at housecleaning.

Federal police were notorious, too. In 2010, 250 officers mutinied against their commander in Juarez, accusing him of planting weapons and drugs on suspects in order to extort money.

“I don’t believe the federal police were extortionists; I know it, personally,” said a Juarez construction contractor who remained in the city, while another 10,000 businesses shuttered.

Human rights observers report Mexican soldiers were themselves engaged in illegal detentions, planting evidence and torturing suspects.

“Yes, the military arrested many people, but they could not make legal cases against them. Most of those arrested were released,” said Arturo Valenzuela, a physician and leader of the We Are Juarez project, a partnership between civic groups and the government.

“The army was not very helpful,” he said.

During the peak violence, the weapon of choice was the AK-47. Attacks occurred in public places. The killings appeared timed to make the evening news broadcasts.

“I remember crime scenes where we would count 300, 400 bullet casings, from different weapons, fired by multiple shooters, with multiple victims,” said David Garcia, director of the Chihuahua State Medical and Forensic Examiner’s Office in Ciudad Juarez.

Crime scene technicians would finish their 18-hour shifts in a daze, like soldiers after combat, having seen too much.

Many assassinations — especially of police or prosecutors — appeared to be the work of trained professionals, who arrived wearing masks and body armor, in convoys, to scout a scene, trap the victims and assure a getaway.

This year, more homicides are committed with smaller-caliber weapons, like 9mm handguns. There are fewer shots fired and less spectacular scenes. Decapitations are no longer common. Many of the dead appear to have been killed earlier, their bodies dumped. It is rare to see a professional ambush.

Julian Leyzaola, chief of Juarez municipal police, said the criminal groups are performing a kind of social “cleansing” by eliminating rival drug dealers, extortionists and carjackers.

In Juarez, it appears someone is mopping up.

Mexican law enforcement officials say many of the 10,500 victims appear to have been hunted down and shot.

“In other parts of Mexico, there are true clashes between the opposing groups. There are firefights, and sometimes innocent citizens are caught in the crossfire. But here in Juarez, the hit men did not confront each other directly. What the assassins did was kill each other’s low-level employees,” said Jorge Gonzalez, the Chihuahua state prosecutor in charge of the Juarez office.

El Diario reported that most of the victims appeared to be unarmed.

In Ciudad Juarez, the newspapers were filled with stories of taco vendors shot tending their stalls, of window washers executed on the street. About one in 10 of the victims was female.

Gustavo de la Rosa, a human rights advocate and researcher at the Autonomous University in Ciudad Juarez, said most of the victims — some 8,000 — likely were involved in “the great pyramid of drugs,” meaning they were members of gangs, sold drugs or consumed them.

De la Rosa bases his estimate on forms his team had family members complete when it accompanied them to claim bodies. He stresses that many of the dead were low-level operatives — recruited from the 14,000 young men in 800 neighborhood gangs.

Teresa Almada, director of Center for the Promotion of Youth, believes the numbers of innocent victims is far higher, and that even those who might have had some involvement in crime were so young and inexperienced as to qualify as innocent.

“They would be recruited; they would be coerced, or forced,” Almada said.

They were cannon fodder.

“Juarez is a city of orphans,” she said.

During the worst violence, many of the bodies at the morgue were unclaimed. They were buried in common graves, their assailants unknown, as case files grew into piles on the desks of prosecutors who brought no more than four cases in 100 before a judge.

The state prosecutor explained he did not have the resources to pursue all the homicides. He said that based on the federal government’s own definition, homicides involving “organized crime,” meaning multiple shoots fired, an ambush, use of stolen vehicles, messages left at the scene — 80 percent of killings in Juarez — should be investigated by the federal government.

“The federal prosecutor has taken less than one percent of the murder cases,” Gonzalez said.

The federal prosecutor conceded his office was pursuing “very few” murder cases in Ciudad Juarez. It appeared the number was near zero.

There have been 580 homicides in Ciudad Juarez in the first seven months of 2012, and so the city is still far from its goal to be the safest in Mexico.

The criminal organizations that brought Juarez to the brink have not disappeared. “What we have seen,” said Peniche, the prosecutor, “is these groups have moved to other parts of the state.”

**Gabriela Martinez in Mexico City contributed to this report.