In the wake of drug kingpin Joaquín “El Chapo” Guzmán’s sensational escape from Mexican prison on July 11, explosive new allegations have emerged about the circumstances of the February 2014 arrest in the resort town of Mazatlán that landed him behind bars. For more than a year, the official story of El Chapo’s arrest has placed elite Mexican marines at the head of the operation, with U.S. federal agencies playing a crucial intelligence support role. However, a new report citing U.S. government sources claims that account is false.

According to leading Mexican investigative newsmagazine Proceso, the agents who arrested Guzmán weren’t Mexican at all — they were Americans, members of the Drug Enforcement Administration and the U.S. Marshals Service, dressed as Mexican marines, working alongside one or more unidentified U.S. intelligence agencies.

Government officials from Mexico and the U.S. have yet to dispute the accuracy of the story, published in the magazine’s July 18 issue, eight days after the world’s most powerful drug trafficker escaped from Mexico’s top maximum security prison, though former officials from both sides of the border expressed their doubts to The Intercept. The magazine’s special features are behind a paywall online.

The Proceso article, by J. Jesús Esquivel, a veteran reporter who has written two books on the history of the DEA and CIA in Mexico, follows anonymous claims from U.S. officials to U.S. media outlets asserting that Guzman’s escape was foretold in warnings provided to authorities in Mexico. Mexican officials have denied these claims.

Filed from Washington D.C., Proceso’s account of Guzmán’s capture is sourced to two U.S. officials whose positions in government are not revealed. Together they claim that his arrest — and much of the intelligence that led to it — was kept secret from Mexican officials until after he was apprehended.

The Mexican constitution places strict limits on the operations of foreign law enforcement, military personnel and intelligence agencies on Mexican soil. In recent years, however, joint U.S. and Mexican counternarcotics operations have pushed those constraints to the brink, with Americans more deeply embedded in the so-called drug war in Mexico than ever before. If true, the Proceso account would represent one of those operations taken to the extreme — with Americans keeping their Mexican counterparts in the dark in order to drive an armed operation to capture Mexico’s most wanted man, in potential violation of Mexican law.

According to Proceso’s sources, U.S. marshals and DEA agents had “perfectly” zeroed in on Guzmán’s “movements” through “interception systems” including satellite tracking in the three weeks prior to his arrest; they were waiting for the right moment to strike. A slew of cartel informants also provided information on Guzmán’s whereabouts, the sources said, adding that these developments were strictly hidden from President Enrique Peña Nieto’s government. Raids on safe houses leading up to Guzmán’s capture additionally yielded “very important information” that was only shared within a trusted circle of Mexican marines, the magazine reports. The sources did not deny working closely with the marines in the hunt for Guzmán — the marines have emerged as the United States’ go-to partner in Mexican counternarcotics operations.

Once the Mazatlán hotel where Guzmán was staying was located, via satellite intelligence, the Americans — including “a group of DEA agents dedicated exclusively to the capture of El Chapo,” along with other U.S. personnel — quickly prepared to act on the information. The Americans did not seek authorization to make the arrest, the sources said, fearing that doing so would doom the operation.

“Agents from the DEA and U.S. Marshal’s Service dressed in the uniform of the Mexican navy, grabbed their weapons, covered their faces in black balaclavas and asked only for logistical support (official vehicles),” the magazine claims, adding that two Mexican marines were posted in the vicinity of the building but were not told exactly where the raid would take place.

Over the course of the next 10 minutes, additional U.S. agents arrived in armored Mexican marine vehicles, the sources said, and moved to the entrance and exit of the building. Pairs of Americans from the DEA, the Marshals and another unidentified U.S. intelligence agency made their way up the stairs of the hotel to unit 401.

Carrying high-powered rifles and door-breaching equipment, the Americans entered the room, the sources said, where they found Guzmán’s only bodyguard, Carlos Manuel Hoco Ramírez, asleep. The U.S. agents reportedly subdued Hoco Ramírez, who then led them to his boss. Guzmán was discovered naked in the master bedroom; his 22-year-old wife, Emma Coronel, lay trembling in bed. With his young twins in an adjacent room, Guzmán reportedly surrendered to the Americans.