The Texas border city of Eagle Pass and the surrounding county are on high alert after 132 inmates escaped Monday through a tunnel dug inside a prison near Piedras Negras, a Mexican city that borders the United States.

“We are very concerned and we have tight security with our border patrol as well as state agencies,” says Maverick County, Texas, sheriff Tomas Herrera. “It would be easy to cross the border area where water is only knee high. We have 80 miles of river. In some places you can swim or walk across.”

“Our officers are patrolling the downtown district, which is right next to the Rio Grande,” says Eagle Pass Police Chief Juan Antonio Castaneda. “We have been very attentive.”

The massive break, which represents almost a fifth of the prison’s population, is one of the largest escapes in Mexico’s history. The Mexican government has dispatched a 70-member special-forces unit as well as Mexican troops to assist local police in the search. The state of Coahuila, where the prison is located, has offered a $15,000 reward for any information leading to the apprehension of an escapee.

On his Twitter account Tuesday, President Felipe Calderón called the jailbreak “deplorable.”

The inmates escaped through a secret, 4-foot-wide by 23-foot-long tunnel they had dug from inside the prison’s carpentry workshop to the prison yard. Once outside, they were able to overpower guards and somehow cut through a chain-link fence into a vacant lot, before disappearing into the rugged terrain that surrounds the 730-inmate facility, which is located about 12 miles from Piedras Negras.

In the U.S., the Texas Department of Public Safety has enlisted state troopers to patrol the border communities, and the U.S. Border Patrol has air boats patrolling the Rio Grande River. “They have choppers looking for them,” Sheriff Herrera says. “We are doing our part by keeping them from coming across.”

Eighty-six of the escapees were serving federal sentences or were awaiting trial for federal offences. “You have drug smugglers, rapists, a little of everything,” Herrera says. So far, three female inmates have been caught. They were discovered hiding in a prison visiting area.

The prison’s director and two other employees are being questioned about their possible involvement in the daring daylight escape. “We will probably hear the warden got 3 million,” says Castaneda, the Eagle Pass police chief. “Whoever was supervising the inmates was probably looking the other way; 132 is a big, large group of people to escape. They had to have help. It was an organized plan. It wasn’t something that came up overnight. It probably took a couple of months to dig the tunnel. It is pretty scary.”

Castaneda believes that corrupt officials may have helped smuggle the digging equipment into the prison. “You would need air hammers,” he says. “It is not easy to dig through there. It is not sandy. It is rocky and the ground is real hard. It is not something you can dig with a spoon. They had to have some pretty good hardware to work on that terrain. They probably had to bring in some good tools, shovels and picks to break through the rock. They were probably taking the bribes for a long time.”

If Castaneda is correct in his assumption, it wouldn’t be the first prison break in Mexican history that involved the help of prison guards. In December 2010, 153 inmates escaped from a prison in Nuevo Laredo with the assistance of 41 guards.

Cartels have also been known to aid in the escape of prisoners. In February, nine prison guards in the northern city of Monterrey admitted they helped 30 members of the Los Zetas drug cartel escape. During the jail break, the Los Zetas killed 44 rival cartel inmates.

Castenada says he believes the Los Zetas or Sinaloa cartels, which have long fought for turf in the area, are behind the latest prison break. “It is a struggle between the cartels to take over the ports and now there is a struggle for who is going to take over Piedras Negras. They are releasing some of their cohorts so they can help them control Piedras Negras,” he says.

“I don’t think at this point that any of the main players here are big heavyweights,” Castenada says of the escaped inmates. “I think they are probably foot soldiers.”

He doesn’t hold out much hope that many of them will be caught. “There is too much money and a lot of hands reaching out for a share of the money,” he says. “The level of corruption runs all the way up, so it is hard to assume they will capture anyone.”

But Sheriff Herrera vows, “We will keep on patrolling the area until we hear they got them all—though he acknowledges, “I think it will be pretty damn hard.”