The Mexican navy gave no details of his purported arrest but was expected to present the alleged drug boss to the media in Mexico City on Thursday morning.

The Matamoros-based Gulf Cartel was once one of Mexico’s strongest, smuggling and distributing tons of cocaine, methamphetamine, heroin and marijuana into the United States under the leadership of the Cardenas Guillen family, three brothers who took over from one another as their siblings were captured or killed.

Costilla was born in Matamoros, across the border from Brownsville, Texas. He worked for several years as a local police officer before joining the Gulf Cartel in the 1990s and became a lieutenant for then-leader Osiel Cardenas Guillen.

After Cardenas Guillen was arrested in 2003 and imprisoned in the US, Costilla joined the capo’s brother Ezequiel in running the cartel. The tumult at the top prompted the powerful Sinaloa cartel to move in from its base along the Pacific Coast and launch a war for control of Nuevo Laredo, the busiest cargo crossing between the United States and Mexico

The Gulf won the fight, backed by a gang of assassins recruited from the Mexican military special forces. Emboldened by their success in holding Nuevo Laredo, the enforcers known as the Zetas began asserting their independence and split from the Gulf Cartel in 2010 after the slaying of a Zeta member in the city of Reynosa, across from McAllen, Texas, that Costilla is believed to have ordered.

The resulting fighting between the two former allies transformed northeastern Mexico, an area home to cattle ranches, sorghum fields and the industrial city of Monterrey into a war zone rocked by daily shootouts and gruesome violence that included decapitations and corpses hung from bridges.

Ezequiel 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 the round-faced, moustached drug trafficker 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, Mario Cardenas Guillen, in the Gulf Coast city of Altamira.

The navy said when announcing Mario’s arrest the cartel had apparently divided into two wings after Ezequiel’s 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 US 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 organised crime.