Mexican drug corruption crosses the border

>>> while much has been reported about the widespread corruption in mexican law enforcement , we have found there is also a serious problem on the american side of the border. with that story tonight, here is mark potter .

>> reporter: in el paso , texas, a major embarrassment for american law enforcement. margarita chrispen is sentenced to 20 years in prison for selling out to mexican drug travellers.

>> it was amazing to us that she received $5 million for her services to allow loads of marijuana to come through her checkpoint along the border.

>> in the mexican drug war , u.s. authorities report 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's the single most debilitating factor in successful law enforcement along the border, and we do a horrible job of weeding that corruption out.

>>> in the last five years, nearly 8y u.s. border patrol agents and customs and border patrol officers have been arrested along the border, and federal authorities say hundreds more officials are undercretion.

>> once they cross the line, they are criminals. criminals that are in our uniform.

>> and the corruption runs deep.

>> the cartels have begun to infiltrate u.s. law enforcement .

>> it was begun during a hiring push five years ago to add officers to the mexican border . only 10% of the initial applicants were given polygraph tests. of those, 60 persz failed, raising the question of the integrity of those who weren't tested.

>> they run into trouble, problems within a year or two or being hired.

>> and for federal authorities aren't the only ones facing problems. local ofls have also succumb to the allure of drug money. these two men were jailed for helping mexican smugglers. in a nearby county, this man said corruption is rampant.

>> it's greed. that's what i said all the time. it's greed. one of the extra $10,000, $15,000, $50,000.

>> president obama signed a law requiring a polygraph test for all border control applicants, and they keep an eye on the 2000 -mile-long border, policing the police.

>> there is no grating problem we're looking at in the organization. we cannot fail.

>> they insist a majority of the border officers are ontstz, and they also say the better they become at stopping the smugglers, the more the mexican cartels rely on corruption, even slipping somef otheir own people into u.s. law enforcement academies. mark potter , nbc news.