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Mexican cartels corrupting more US border officials?

In the Mexican drug war, U.S. authorities are finding a disturbing trend: an increase in American law enforcement officials corrupted by wealthy Mexican criminals.

Editor's Note: This is the latest in Mark Potter's War Next Door series, a string of reports about the deadly drug war raging in Mexico and along the U.S. border. Click here for more news from the region.

In El Paso, Texas, a major embarrassment for American law enforcement: U.S. Customs and Border Protection officer Margarita Crispin is sentenced to 20 years in prison for selling out to Mexican drug traffickers.

"It was amazing to us to find out that Margarita Crispin received $5 million for her services to allow loads of marijuana to come through her checkpoint along the border," assistant director of the Criminal Investigative Division of the FBI, told NBC News.

In the Mexican drug war, U.S. authorities are finding a disturbing trend: an increase in American law enforcement officials corrupted by wealthy Mexican criminals who pay them to look the other way as illegal drugs and immigrants flow north into the United States.

"It is the single most debilitating factor in successful law enforcement on the border, and we do a horrible job of weeding that corruption out,” says retired DEA supervisor Anthony Coulson.

In the last five years, nearly 80 U.S. Border Patrol agents and Customs and Border Protection officers have been arrested along the Mexican border, and according to federal authorities, hundreds more officials are under investigation.

“Once they cross the line, they are criminals, criminals that are in our uniform,” explains Customs and Border Protection Deputy Commissioner David Aguilar.

Corruption runs deep
At a U.S. Senate hearing, it was revealed that Mexican cartel members are infiltrating American law enforcement. There was also testimony that during a hiring push that began five years ago to add thousands of Border Patrol and CBP officers, only 10 percent of the initial applicants were given polygraph tests.

Of those, 60 percent failed, raising concerns about the integrity of the others hired without screening.

"A very large percentage of those they don't test run into trouble within a year or two of being hired,” says Sen. Mark Pryor, D-Ark..

Along the border, the federal authorities aren't the only ones facing corruption problems. Local authorities, including sheriffs and police officers, have also succumbed to the lure of drug money.

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In South Texas, former Sheriffs Conrado Cantu and Reymundo Guerra were jailed for helping Mexican smugglers, while in nearby Zapata County, Sheriff Sigifredo Gonzalez says corruption is rampant.

"It's greed, that's what it's been all the time, it's greed. It's just wanting that extra $10,000, $15,000, $20,000," Gonzalez explains.

Policing the police
To try to stem the corruption, President Obama recently signed a law requiring polygraph tests for all border patrol and customs law enforcement job applicants. Additionally, thirteen FBI anti-corruption teams now keep an eye on the 2,000-mile-long border, policing the police.

"There is no greater problem we are looking at within this organization. We cannot fail,” Aguilar declares.

Authorities insist the vast majority of border officers are honest and work hard in dangerous conditions, but they also say the better they become at stopping the smugglers, the more the Mexican cartels rely on corruption.