Ezequiel Cardenas was the cartel's figurehead until he was killed in November 2010 in a shootout with Mexican marines in Matamoros. Authorities believe Costilla controlled the cartel's daily drug trafficking activities but kept a low profile. Only two photographs of him were ever made public.
HIs removal from the scene could serve as an opening for Sinaloa or the Zetas, who have become the nation's dominant cartels, to move in on smuggling routes that have been believed to include the border cities of Reynosa and Matamoros, and the Gulf port of Tampico.
El Coss's capture would be a significant victory for the marines, who were embarrassed in June after announcing they had nabbed the son of Mexico's top fugitive drug lord.
It turned out the man wasn't the son of Joaquin "El Chapo" Guzman, but rather Felix Beltran Leon, 23, a stocky, baby-faced suspect whose family said he was the father of a toddler and worked with his mother-in-law at a used car dealership. He remains in custody, authorities say, because guns and money were found when he was arrested.
The announcement of Costilla's arrest comes just more than a week after the navy said it had detained another brother of Osiel Cardenas Guillen, Mario, in the Gulf Coast city of Altamira.
The navy said in announcing that arrest that the cartel had apparently divided into two wings after Ezequiel Cardenas' death.
Arrests of high-ranking cartel leaders often lead to detentions of others, some because officials find intelligence with the suspects, others because detainees swiftly turn against their former comrades and provide information that leads to their arrest.
In November 1999, a Drug Enforcement Administration agent and an FBI agent, both assigned to the U.S. consulate in Monterrey, had been followed by a car through Matamoros until a truck cut them off.
They were quickly surrounded by about a dozen heavily armed men, allegedly including Costilla and Osiel Cardenas Guillen, who threatened to kill them. The agents eventually persuaded the gunmen to let them go.
Costilla was also linked to the August 2004 beating death of Matamoros newspaper columnist Francisco Arratia Saldierna, who reported on drug trafficking and organized crime.
Correspondent Michael Weissenstein in Mexico City contributed to this report.
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