Almoloya de Juárez (Mexico) (AFP) - It was meant to be an impenetrable fortress to keep Mexico's most infamous murderers, kidnappers and drug lords behind bars for most of their lives.
But Sinaloa drug cartel kingpin Joaquin "El Chapo" Guzman became the first inmate in recent memory to slip out of the Altiplano maximum-security prison, some 90 kilometers (55 miles) west of Mexico City.
Despite security cameras trained on his cell, Guzman managed to vanish into the night on Saturday, after slipping into his shower and climbing down a secret hole leading to a 1.5-kilometer (one-mile) long tunnel that ended at a construction site.
It was his second prison break in 14 years. He last fled from a maximum security prison by hiding inside a laundry cart in Jalisco state in 2001.
Surrounded by cornfields in the central State of Mexico, the Number One Federal Social Rehabilitation Center was built during the 1988-1994 administration of president Carlos Salinas.
The 724-capacity facility covers a surface of 26 hectares (64 acres), with the actual prison accounting for 2.8 hectares of that space while the rest is used for the security perimeter, according to a document from the now-defunct public safety ministry.
The prison has eight dormitories, cafeterias, classrooms and sports facilities. It includes areas for family and lawyer visits as well as courts.
"The center has a maximum security level and it has electronic systems and equipment such as closed-circuit television; controlled access; alarms; metal, drug and explosive detectors," according to the ministry, which has since been replaced by a new federal security agency.
On Sunday, a federal police officer told AFP that the prison has "three concrete walls" forming a thick security perimeter. Four surveillance towers rise above the grounds.
Following Guzman's escape, 18 prison guards were interrogated by prosecutors, as corruption of wardens is common in Mexico.
The prison houses other notorious criminals.
Guzman's neighbors included some of his enemies, such as Zetas drug cartel boss Miguel Angel Trevino and his brother Omar Trevino.
One of the newest guests is Servando "La Tuta" Gomez, the leader of the cultish Knights Templar drug cartel, who was considered Mexico's most wanted man when he was caught earlier this year.
In March, Guzman and some 140 other prisoners sent an 11-page, handwritten letter to the governmental National Human Rights Commission, claiming that they found worms in their food and that the mattresses in the rooms for conjugal visits were filthy.
In addition to Guzman, the letter was signed by the head of the Beltran Leyva crime family, Hector, who was captured last year, as well as the US-born capo Edgar "La Barbie" Valdez.
A small dent in the prison's armor emerged in March, where authorities said a woman managed to see Guzman by using a fake ID to get in.