The reach of Mexican drug cartels doesn’t stop with the legions of people murdered or the many communities destroyed. It extends across the Rio Grande and into the ranks of U.S. Customs and Border Protection officers, some of whom sacrifice their integrity and endanger the nation’s security in exchange for favors.

Compounding matters, federal law enforcement agencies have engaged in a turf battle over who should conduct the corruption investigations.

On Thursday, a special Senate panel will try to sort this out.

“Fighting corruption is vital to protecting our borders and securing our communities,” said Sen. Mark Pryor (D-Ark.) , chairman of the Senate Homeland Security and Governmental Affairs ad hoc subcommittee on disaster recovery and intergovernmental affairs. “We must be aggressive in rooting out corruption within our U.S. law enforcement agencies.”

Pryor, however, is concerned about the level of cooperation among law enforcement agencies probing that corruption. He warned Homeland Security Secretary Janet Napolitano in an April 2010 letter of “coordination and information sharing problems” between DHS investigative units.

Before we get to that drama, here are some facts.

The DHS inspector general’s office has 267 active investigations of CBP employees who have been accused or suspected of corruption. This represents 44 percent of the office’s investigations of CBP staff members and is, by far, the largest category.

Since October 2004, 127 CBP officers have been arrested or indicted on corruption charges. Just last month, former Border Patrol agent Yamilkar Fierros of Tucson was sentenced to 20 months in prison for taking $3,000 from a suspected drug dealer in exchange for a list of 109 Border Patrol sensor locations in the Sonoita, Ariz., area. He also was indicted for accepting $1,000 in return for a sensitive law enforcement map and $1,500 to help a dealer move a load of drugs to Tucson.

Last year, a CBP technician named Martha Garnica was sentenced to 20 years in prison on charges that included bribery, conspiracy to import 100 kilograms of marijuana and conspiracy to smuggle in people.

Of course, the vast majority of CBP officers “serve our country with great distinction and integrity every day,” as CBP Commissioner Alan D. Bersin said in testimony prepared for Thursday’s hearing.

But that’s not the whole story.

“I fully acknowledge that the agency has suffered from the corruption of employees that have disgraced the service and betrayed the trust of the American public and their fellow officers, agents and mission support personnel,” Bersin said.

What also has suffered is the level of cooperation among officials who go after their corrupt colleagues.

As the Center for Investigative Reporting wrote in The Washington Post last year, in December 2009, Thomas M. Frost, an assistant inspector general, told James F. Tomsheck, the CBP assistant commissioner for internal affairs, to stop investigating suspected criminal actions by CBP employees. In no uncertain terms, Frost’s memo said: “I direct that as of this date, your office cease criminal investigation of any matter involving a DHS program or employee.”

In case that wasn’t clear enough, Frost demanded a list of all such probes within five days. After his office reviewed that list, Frost said, “I will contact your office with a list of matters on which you should proceed, should there be any.”

Charles K. Edwards, the DHS acting inspector general, plans to tell the hearing that the internal affairs office has a “crucial complementary role” to the inspector general’s criminal investigative function. That complementary role includes pre-employment investigations of applicants. But it is his office, he says in prepared testimony, that has “the authority and responsibility within DHS for investigating allegations” of corruption.

Friction between the two agencies remains, with the inspector general’s office complaining that the internal affairs office continues to conduct criminal investigations of DHS employees even though it lacks the legal authority to do so.

The acting inspector general also was not happy with an FBI plan that he felt did not recognize the inspector general’s “statutory authority as the focal point for all criminal investigations of employee misconduct within DHS.” That plan has been withdrawn and the agencies continue to negotiate.

“We can only achieve results if investigations are conducted in an efficient and collaborative manner,” Pryor said. “Based on reports, we’re not there yet.”