In the Mexican border city of Juárez the question persists: What kind of involvement did the United States government have, or not, with the turf war between drug cartels that claimed thousands of lives only a short drive across the Rio Grande from El Paso? Three years after the worst of the carnage, details about the U.S. role gradually are beginning to surface.

When agents of the U.S. Federal Government try to penetrate the underworld along the Mexican frontier, the risks are high that, while they’re investigating it, they'll get sucked into it. In the so-called “Fast and Furious” Affair exposed in 2011, the Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) wound up helping the cartels build their substantial arsenals.

But gun-trafficking is not where the story ends. There are numerous allegations that federal agencies fighting the drug trade have, in fact, facilitated the trafficking by certain cartels. And worse: that they took sides in their wars, helping one cartel against another in an orgy of bloodletting. In Ciudad Juárez, Mexico, from 2007 to 2010 the number of murders jumped from 300 to more than 3,000. That was precisely the time period in which collaboration between at least one federal agency and one cartel in the Juárez wars was at its closest.

“Get sideways” is cop slang for breaking the law. It is most commonly applied to informants who want to have the thing both ways. They want the benefits of being an informant and the income from doing something illegal. And some of the masters of the sideways maneuver are connected with the Sinaloa cartel, whose legendary leader Joaquín Guzmán Loera, known as El Chapo, was arrested in Mexico this year.

One sideways example: The son of another Sinaloa kingpin made headlines alleging in court in Chicago that his father’s cartel received “carte blanche” from the United States government to continue to smuggle illegal cocaine by the ton into the country. U.S. officials denied this.

The Feds also deny unconfirmed claims arising from the case in Chicago that they permitted informants from the Sinaloa cartel to attend meetings where the cartel was discussed, or warned them of anti-drug operations planned in the cartel’s territory. By way of proof, they point to the plethora of top Sinaloa leaders captured and prosecuted in recent times, culminating with the arrest of El Chapo.

There is in fact substantial evidence and testimony suggesting that the ICE (Immigration and Customs Enforcement) facilitated major drug shipments by its informers in Mexico’s Sinaloa cartel in 2007 and 2008 by giving them visas for easy entry to the United States.

This was at a time when El Chapo’s Sinaloa cartel was mounting an all-out offensive to take over the territory of the Juárez cartel near El Paso. And the deadly consequences of that de facto collaboration between a U.S. government agency and a cartel kingpin can be felt on the border to this day.

In February, a former hit man for the Juárez cartel testified that he had coordinated the assassinations of three individuals linked to the U.S. consulate in Juárez in 2010 as retribution for favorable treatment to its enemies in the Sinaloa cartel. He said the Juárez cartel noticed that its enemies were able to sell cocaine at an usually low price in El Paso, and suspected the reason was that someone in the consulate was giving away visas to enable members of the Sinaloa cartel to move drugs more easily into the country. In April, a whistleblower from the U.S. Bureau of Diplomatic Security told Newsweek magazine he suspected a top regional security officer in the Juárez consulate of making improper visa referrals that put consular employees in danger of violent reprisals.

In a review of thousands of pages of federal court records, police reports, and court testimony from the trial of a Sinaloa cartel trafficker named Fernando Arambula, as well as interviews with dozens of sources in Juárez familiar with the cartel war, our reporting shows this U.S. strategy directly served the interests of El Chapo and the Sinaloa cartel.

The documents trace back to the early stages of the strategy in Juárez, as federal agents attempted to build a network of informants who held positions of authority in the Sinaloa cartel.

For two decades, the Juárez cartel controlled the movement of drugs in the northern Mexican state of Chihuahua near the Texas and New Mexico borders. To hear locals tell it, the cartel maintained order over the law itself—over the army, the police, the federal agencies, the state and the city. And one of the Juárez kingmakers was an ex-cop turned businessman named Julio Porras.

Porras owned a currency exchange and a construction company. People say he owned a stake in a bar called The Boiler. They found out later he was publisher of the magazine Two Faces . His criminal associates knew him as Old Timer and they say he was once the key link between the Juárez cartel and the high command of the state police in Chihuahua.

But in 2006 Porras made a near-fatal strategic mistake. El Chapo Guzmán's men wanted to control as much of the border traffic as they could. Simple geography suggests their problem. Their base of operations in Sinaloa was on the sea, which was useful for smuggling, but they were nowhere near the U.S. market. So they started moving in on the Juárez “plaza,” as the drug corridors are called. Porras looked at the situation and advised the boss of the Juárez cartel, Vicente Carrillo Fuentes, alias The Viceroy, to seek a diplomatic solution to the crisis.

But no diplomatic solution would be forthcoming. Shortly after Porras’ audience with El Viceroy, a team of 15 gunmen ambushed his security convoy as it pulled to a stop in front of his house. His driver and two state policemen he employed as bodyguards were killed. Porras escaped with a bullet wound in the left arm. Porras took off for El Paso. He bought a garage and he offered a refuge or sorts to a faction of the Juárez cartel that threw in its lot with El Chapo. They called themselves Gente Nueva, New People.

As it happened, at just this time a special investigations group from the ICE in El Paso had started collecting information to target the Juárez cartel. Porras had plenty of that, and was happy to oblige. Criminal associates of his from the time have testified that El Chapo authorized his men to cooperate with the ICE’s program against the organization of El Viceroy.

One of El Chapo’s operatives was José Esparza, the head of a drug distribution ring that moved cocaine, crystal meth and marijuana into the United Stated via El Paso. Porras recruited Esparza to be an ICE informant because he wanted “to bring people over that belonged to the cartel, so they can talk about Vicente Carrillo’s people,” Esparza testified at the trial of another former El Chapo lieutenant.

Things quickly got sideways.

At the time Esparza was an ICE informant, he was trafficking 1,600-pound loads of marijuana to customers in Detroit and Atlanta. He had recently hauled a 1,000-pound load of marijuana to Muskogee, Oklahoma, in a trailer filled with piñatas.

It was understood—indeed, Esparanza said that Porras made it explicit—that Esparza wasn’t to tell the ICE agents about any of this, and they probably wouldn’t press him too hard. “What Julio Porras had told me, if they asked—ICE would ask me if I was moving dope, to tell them I was not moving anything,” Esparza explained to the court.

In case Esparza missed the point, Porras hammered it home again when they got together at a Diamond Shamrock gas station in front of the ICE offices, right before Esparza was to meet with the agents. Esparza didn’t want to go to the meeting at all, but Porras insisted. It was vitally important, as it were, to make nice with ICE.

If ICE was facilitating visas, El Paso would become in effect the strategic depth for El Chapo’s people in their war on The Viceroy and the Juárez Cartel.

The El Chapo strategy was to take out the Mexican police commanders who protected The Viceroy in Juárez, according to Esparza. “Julio Porras was recruiting people to come over and talk to ICE, so they can get control of Juárez and start knocking off the commandantes,” Esparza testified.

Two Mexican police captains and a commander were shot to death in Juárez within a 24-hour period on January 21 and 22, 2008. The killers used military-grade weapons and ammunition. Anonymous sources in the state government told El Diario de Juárez that the attacks were the work of El Chapo Guzmán.

On January 26, 2008, a flowered wreath appeared at The Monument to the Fallen Policeman in Juárez, along with a message scrawled on white pasteboard: “For those who didn’t believe,” and a list of the murdered policemen. Below it was a second message, “For those who still won’t believe,” and the names of an additional 17 Juárez police officers.

Porras and Esparza were only two of El Chapo’s men who entered the United States freely to meet with the ICE. The cartel men kept the phone numbers of ICE agents on their prepaid cellphones. Esparza recalled that they brought photographs and helped agents to identify the faces of the Juárez enemy. And all of the El Chapo informants were moving drugs into the United States at the time that they were meeting in person with the ICE’s team in El Paso, according to their testimony in a pivotal court case in 2010.

The trial of Fernando Arambula, a top El Chapo lieutenant, exposed the relationship between the Sinaloa cartel and ICE to public view, even though few news organizations picked up on it at the time.

Arambula represented himself as the information officer for El Chapo. Another informant, Jesus Manuel Fierro, referred to his and Arambula’s role as the cartel’s go-to people for ICE: “There were two of us who were like—like spokespersons. We were passing all the information. But this information we would, obviously, get from the levels high up.”

At the same time, Arambula was having loads of marijuana that weighed 20 tons delivered by air and unloaded by a crew of 60 laborers at his ranch in Ascencion, Mexico, and a large estate in the border town of Palomas, Mexico. Arambula also had an office in Juárez where a dozen employees used a hydraulic press to package the marijuana into 10-pound bricks.

ICE Special Agent Louie Gomez, who was Arambula’s handler, called him the most connected high-level trafficker he had ever known. A tip from Arambula in March 2007 netted the agency The Tiger of the Sierra, a wanted trafficker whose real name was Pedro Sanchez and who was, of course, an El Chapo rival.

Special Agent Gomez testified at Arambula’s trial that the new informants happened to arrive at ICE’s door just as the Juárez cartel investigation was getting on track. He said the agency tried to work on cases related to both the Juárez and Sinaloa cartels and that the Juárez cartel investigation was underway for quite some time.

“You know, whatever comes our way, we’re going to investigate it,” said Agent Gomez. “I mean, it just happened to be that the Juárez cartel was—that was the case we were working on at the time.”

At least one of the informants for the ICE special investigations group had blood on his hands. Mario Nunez Meza, alias M10, alias Mayito, a former municipal police officer who became El Chapo’s plaza boss in Chihuahua and Durango. In Juárez, locals regard him as the commander of the ultra-violent Sinaloa offensive in their city.

The Mexican Justice Department holds M10 responsible for 388 murders, and he has been linked to 23 mass graves discovered in his home state of Durango. He is wanted by Interpol and was indicted for drug trafficking in 2012 by the U.S. District Court of El Paso.

M10 was captured last year during a raid by Chihuahua State Police on a stash house in Juárez. Police found bulletproof vests, ammunition, and 14 explosive devices made of the water-gel Tovex. A news report of his arrest described armored personnel carriers from the Mexican army standing guard outside the police station where he was being held for questioning.

M10 has a musical ballad named after him that the band Los Sembradores de La Sierra recorded in 2011. Its opening lines urge the listener to put on body armor, grab hold of machine guns and grenades, and prepare to go to war with M10, whom the lyrics address directly in one verse:

Your codename M-10

Is all the rage these days

It might as well have been a flag

For all the blood it cost

But in 2007 and 2008 M10 entered the United States freely to meet with the ICE, no questions asked, according to the ex-police captain, Fierro. “I don’t know how they did that,” Fierro testified.

José De Jesus was the group supervisor for the ICE program that targeted the Juárez cartel in 2007 and 2008. He was promoted and transferred to ICE headquarters in Washington a year after the special investigation wrapped up. When Fernando Arambula’s case went to trial in March 2010, De Jesus was the highest-ranking ICE official to testify. But the ICE only consented to have him testify on the condition that he would not answer questions about the agency’s confidential-informant program.

De Jesus testified at trial that ICE management in El Paso was supportive of how he handled the investigation. And he waltzed around the question of Arambula going sideways. He said ICE made it clear to Arambula that he could not engage in illegal activities while he was an informant for the agency: “We had other plans for Mr. Arambula, not only to work the Juárez cartel, but we wanted him to, in reality, work the Sinaloa cartel for us,” De Jesus testified.

According to De Jesus, ICE management soured on Arambula for reasons that he did not make clear during his testimony. Eventually management stepped in to end Arambula’s term as an informant in October 2010.

By then De Jesus had already received orders to distance himself from Arambula. “We had Mr. Arambula on kind of like timeout, if you want to call it that, for the simple fact that my management had told me—had told us—to minimize the amount of contact we had with him.”

On October 9, 2010, De Jesus was notified by agents in the ICE office in Demming, New Mexico, that a warrant had been issued for Arambula’s request. The next day, Agent Gomez called Arambula to meet him at their usual place, a Baskin Robbins in El Paso. Arambula was arrested on arrival. The ICE agents from Demming handled the post-arrest interview. De Jesus had no further dealings with Arambula. At trial, the U.S. Attorney’s Office refused to take Arambula’s record of cooperation with ICE into account, to the chagrin of Arambula’s lawyer, Martha Eskesen.

“He provided cooperation to the government, nevertheless, the government is seeking numerous sentencing enhancements, requests a life sentence, and will not seek any mitigating departures or variances,” Eskesen wrote in a court brief. She declined to be interviewed about the case for this story.

In a separate filing, Eskesen refers to a document attesting that the United States Attorney’s Office approved a benefit for Arambula to be able to move freely back and forth across the border, though he is not an American citizen, so he could better serve as an informant. She goes on to observe that the approval came from former Assistant U.S. Attorney Margaret Leachman, the wife of Russell Leachman, the lead prosecutor in Arambula’s trial in March 2010.

On the witness stand, De Jesus downplayed the amount of cooperation his group ever received from Arambula. “We didn’t get to a point where he could actually help us in a major manner,” he said. “Yes, he did provide some information. Basically, during those times, we were just vetting him to see what type of information he had.”

Agent Gomez testified the ICE spent no more than 15 hours with Arambula in total. But Arambula visited the ICE offices in El Paso on at least two occasions, and met with Agent Gomez alone on several others. The ICE had to commit extra time to Arambula in part because concerns for his safety meant ICE would escort him to border crossings sometimes as far as two hours away from El Paso. Special Agent Xavier Diaz testified he once drove five hours west of the city to meet Arambula in Nogales, Arizona.

Arambula was sentenced to life without parole. And he was not the only Sinaloa cartel informant to suffer an abrupt reversal of fortune with ICE. On the day of Arambula’s arrest, DEA agents raided the house of Manuel Fierro in El Paso. Eventually he was sentenced to 27 years—then his sentence was reduced as a reward for his court testimony in Arambula’s trial a month later in El Paso. He is due for release from FCI Beaumont Low in August 2016

Gary Hill is an El Paso criminal defense attorney who represented Fierro in Indiana. At Fierro’s sentencing he remarked on how strange the entire case had been, implying carefully, but not stating, that there was some sort of cover-up in the works.

“What had happened was that they took him up to a certain point, and then they just said—they kind of let him go,” said Hill. “They told him right at the end of the thing, they said, ‘This is just too big for us, we can’t deal with it.’ And they just walked away, I mean, right in the middle of all of this.

“There’s some concern on the part of the authorities in El Paso, the federal authorities in El Paso, that there was some maybe collusion, cooperation, something, between some of these agents and the people in Juárez.”

Hill could not be reached for comment for this article.

Agent Gomez testified to a concern in the ICE investigations group that his informant Fernando Arambula was getting sideways

It was not that Arambula concealed from agents the fact that he was a lieutenant for El Chapo Guzmán in Juárez. Arambula had information useful to the ICE because he was a criminal. “It wasn’t so much we had doubts that the information was good,” Gomez testified, “it was we had doubts about his intentions.”

Under cross-examination from Martha Eskesen, Gomez confirmed that his team had received information that United States agents with a different agency—unnamed—had gotten sideways in Juárez: “We got some information, yes. We got some information and then we passed it along. We don’t—we don’t investigate it. We just get the info and we pass it.”

El Chapo was arrested by a special contingent of Mexican Marines in February. Although the carnage in the Juárez area has diminished, on May 25 two armed men entered the law office of the ex-president of the local bar association and gunned him down along with a municipal judge who was with him at the time. Border security analysts interpret the murders as a settling of old scores by the Juárez cartel, which has gained in strength and boldness and apparently intends to retake the territory it lost in the war with El Chapo and the ICE.