Over 130 inmates burrowed out of a Mexican prison yesterday, in one of the country’s biggest jailbreaks in recent years. The prisoners—who were held in the city of Piedras Negras, just across the border from Eagle Pass, Texas—escaped through a tunnel that was 21 feet long and four feet across, before cutting through a chain-link barrier to a neighboring property. The tunnel “was not made today," explains Homero Ramos Gloria, the Coahuila Attorney General, helpfully. "It had been there for months. The prison was not overcrowded; none of our prisons are. We have 132 inmates escaping through a tunnel, and it doesn’t make sense.” Some are speculating that prison officials may have aided the inmates, and the director and two other employees of the prison have been detained for investigation. The prison holds about 730 people—meaning that this escape involved almost one fifth of its population. Of the 132 escapees, 86 were serving sentences or awaiting trial for federal crimes such as drug trafficking. Members of Mexico’s drug gangs frequently attempt to bust out their incarcerated members, and guards are often accused of working with the cartels—in December 2010, 153 inmates escaped from a prison in Nuevo Laredo, and 41 guards were charged with helping them. And of course, Mexican cartel members tend to be well-equipped with tunneling skills.