A covert U.S. operation sending manned aircraft south of the border has assisted Mexican police identify, capture and kill some of that country's most wanted criminals, according to sources.

Under the direction of the Pentagon's Northern Command, "Operation Lowrider" began in 2011 after the death of U.S. Immigration and Customs Enforcement agent Jamie Zapata.

"It's been successful in identifying, eliminating and bringing to justice those who brought tons and tons of drugs in to the United States," says Phil Jordan a former DEA special agent and director of the agency's El Paso Intelligence Center.

Unlike drones operated by the Department of Homeland Security, the two prop planes are manned by a subcontractor to Sierra Nevada, a U.S. defense contractor, according to the website vocative.com. Using advanced eavesdropping equipment, "pattern of life" reconnaissance missions expose the schedules and routines of high level traffickers. That information is passed on to U.S. officials who contact Mexican police or military units to apprehend the target.

"I'm told that they fly daily and as much as possible. They land, they refuel, they get their maintenance and they get out again," says voactive reporter Aram Roston. "They're highly trained. They fly these planes in patterns over a target's house. In the back of the plane are technicians who man the earphones, electronics and camera."

The operation is not without risk. Two U.S. surveillance planes crashed on similar missions in Colombia 10 years ago. Guerillas killed a U.S. pilot and kept three Americans in captivity for six years. That $8.6 million operation was also undertaken by a defense contractor, Northrup-Grumman.

Asked about the classified operation, Northern Command spokesman John Cornelio said, "We work closely with the Mexican military and assist them whenever we can because it is in our best interest and theirs. We have been involved in sharing equipment, information and other activities. However, information sharing is not something we discuss."

For decades the U.S. has assisted Mexican in the drug war. Overtime, America has trained their police, run AWACs off their coast, shared wiretaps and undercover agents' intelligence.

"This is just another tool the government has at its disposal," says Jordan. "Anytime we can take those people off the radar it helps American law enforcement. It helps the DEA and it helps the Mexican Government."

Voactive reports some corrupt cops tipped off cartel bosses of impending raids, despite almost real time intelligence. The contract with Sierra Nevada expires in September. It is unknown whether Northern Command will renew it, or if President Enrique Peña Nieto will continue to give the American surveillance flights permission to enter Mexican airspace.

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William La Jeunesse joined FOX News Channel (FNC) in March 1998 and currently serves as a Los Angeles-based correspondent.