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The house itself is not much to look at. Built on seemingly unused pasture next to a creek, surrounded by corn fields and with a clear view of Altiplano, Mexico's maximum security federal prison, the building is little more than a small construction of concrete bricks and a metal gate, surrounded on all four sides by a low wall.

A heavy contingent of soldiers and policemen prevent entry to the interior of the building, but a quick glance through a hole in the wall shows an empty space, littered here and there with construction materials. In the middle of the room the floor opens up, a square hole no bigger than a square meter. But it was all the space Joaquín 'El Chapo' Guzmán, Mexico's most wanted drug lord, needed to crawl to freedom after escaping Altiplano through a mile-long tunnel.

The building shows no sign of habitation and appears to have been built solely for the purpose of getting Guzmán out of prison. That may be exactly the case. As Mexican authorities scramble in a massive manhunt to recapture the drug lord, details begin to emerge on the scale of the operation that broke out the nation's top public enemy.

A report published Monday by Mexican website Animal Político, based on comments by anonymous law enforcement officials, chronicles a massive operation by Guzmán's organization to execute the prison break which took some 12 months of planning.

Many people and resources were inevitably involved, but as one of the founders of leaders of the Sinaloa Cartel, one of Mexico's oldest and most powerful criminal enterprises, Guzmán may well have had all the resources he needed at his disposal. Though a disputed claim, Forbes once listed him as a billionaire and among Mexico's richest men.

Residents of the nearby Santa Juana neighborhood of Almolaya de Juárez told Animal Político that a 'robust and relaxed' man approached them in May last year and told them 'his boss' ordered construction work on the hill. During the following months, those involved in constructing the tunnel and the building hiding its exit kept a low profile.

Trucks would come and go on a regular basis, but according to the website residents were generally not bothered by the construction work, even though anonymous law enforcement officials hinted that several families living nearby were threatened by those involved in the operation.

As discrete as the construction work was carried out, it would have been impossible for Guzmán's accomplices not to have been seen regularly. The hill on which the concrete building was built is located to the southeast of Altiplano and relatively isolated, but in plain view of both the prison itself and a nearby residential area.

Approaching the site is not easy, however. The two dirt roads leading to the area are muddy and uneven. The first route, south of the site, lies closest to Santa Juana. Curious residents would have had to stumble through almost a mile of corn fields and soggy grasslands and jump a narrow creek to get to the hill.

There is a second, more isolated road approaching the structure from the north and ending right on the driveway of the building. That pathway, however, seems to have been constructed far more recently and specifically to allow a getaway car to park right outside and provide Guzmán with the means to escape immediately after exiting the building.

Law enforcement officials interviewed by Animal Político say that, for now, the authorities assume that was the scenario by which the drug lord could get away. They discarded the possibility he would have escaped by helicopter.

The tunnel itself, which ends in the shower area of the prison, is equipped with a ventilation system, electrical wiring and even a customized motorcycle placed on a rail, which authorities assume was used to remove the excess dirt while tunneling to the prison.

It still unclear who exactly was responsible for the construction work. No one seems to know who owned the property on which the building was constructed and the tunnel dug. The area surrounding the building is mostly inhabited by impoverished corn farmers, and Mexican media report many have illegally built their homes on land they do not own.

Nor is it clear what degree of involvement prison employees may have had in the prison break. So far, 30 people working at Altiplano are held for questioning, including the prison director. Their status as suspects or witnesses is still being determined, Mexican federal attorney Arely Gómez said in a short statement Sunday after visiting the building from which Guzmán escaped.

Shortly after news of Guzmán's escape broke, interior secretary Miguel Ángel Osorio Chong hastily returned to Mexico from France, where he had accompanied president Enrique Peña Nieto on a state visit. He has taken charge of the search effort and was set to reveal more information in a press conference Monday night.