More than 140 Customs and Border Protection agents were arrested or convicted of corruption in recent years—and President Trump’s promise to hire 5,500 new agents could make the problem worse.

SOUTH PADRE ISLAND, Tex.—In the calm waters of the Texas Gulf Coast, Robert Hannan steered his boat toward what he thought was a crab trap. He found a corpse.

“There’s nothing that can help this person if it's a real body,” Hannan said in disbelief to the 911 dispatcher. “It's floating just like it would a body, but there’s no head.”

That grisly find would lead investigators first to an assassin from the powerful Gulf Cartel, and then to a U.S. Border Patrol agent who helped the killer move drugs and guns across the border.

Joel Luna is one of more than 140 Customs and Border Protection agents arrested or convicted on corruption charges in the past dozen years, according to an analysis by the Center for Investigative Reporting and The Texas Tribune. “Mr. Luna is not one bad apple,” said James Tomsheck, a former senior official at CBP. “He is part of a rate of corruption that exceeded that of any other U.S. federal law-enforcement agency.”