Customs and Border Patrol agents keep catching the same drug trafficker on the southern border whose brother happens to be a senior CBP agent, and Senate investigators want to know if the illegal immigrant has been getting special treatment.

The case involves Miguel Angel Padilla Heredia, a Mexican citizen with a history of robbery and drug smuggling who has been arrested repeatedly at the border of Arizona and Mexico. At one point, Padilla tried to claim eligibility for the deferred action policy that President Obama announced in 2012, but he was ordered deported, only to return in December 2013.

Padilla was stopped at a border patrol check point and "allegedly narcotics were discovered in his vehicle," but he wasn't deported.

"It is unknown what occurred during this specific interaction, and whether this was the first instance in which Mr. Padilla attempted to smuggle narcotics into the United States," Senate Homeland Security and Government Affairs Committee Chairman Ron Johnson, R-Wis., wrote in a July 26 letter to Department of Homeland Security Inspector General John Roth.

What is known, however, is that the alleged drug smuggler's brother, Manuel Padilla, was chief of the Tucson Sector of the U.S. Border Patrol when he was stopped at that checkpoint. The CBP officer is now a chief patrol agent for the Rio Grande Valley Sector.

Johnson wants Roth to investigate the immigrant's interactions with the Border Patrol to learn more about his most recent stop at the border checkpoint and find out if the border patrol chief had "any influence" on his brother's case.

"While the committee is not aware of any direct evidence that Chief Patrol Agent Manuel Padilla took any action on behalf of his brother, the fact that his brother allegedly entered the country illegally during the time of Chief Patrol Agent Padilla's leadership of the Tucson Sector raises concerns," Johnson wrote to Roth.