Sutton later filed an indictment against a cartel lieutenant, Heriberto Santillan-Tabares, for drug trafficking and five murders, though the murder charges were later cancelled by Sutton in a plea bargain.

Valdez worked for several years as a cartel lieutenant before rising to a leadership position in an enforcement squad called Los Negros.

"They don't know cartel lieutenants," Ms. Williams said.

On April 22, 2010, a cartel lieutenant Gerardo Alvarez-Vazquez was captured on the outskirts of Mexico city; the U.S. had been offering a $2 million U.S. bounty for his arrest.

Arnoldo Rueda Medina aka La Minsa is one of three cartel lieutenants was capture in Morelia, Michoacán.

Migrants and the organizations that assist them say cartel lieutenants roam the shelters, looking for deportees willing to work as lookouts, earning $400 a week until they have enough to pay for passage north.