Teodoro Garcia Simental was arrested nearly a month ago
Mexican police and troops have arrested two men suspected of heading a drug gang operating in the city of Tijuana, on the border with the US.
In two simultaneous operations, security forces targeted Manuel Garcia Simental and Raydel Lopez Uriarte.
Their arrest follows last month's capture of Mr Garcia Simental's brother, Teodoro.
Their gang is believed to have carried out hundreds of killings amid violent turf wars between rival cartels.
Teodoro Garcia Simental, "El Teo", is reported to have broken off an alliance with another cartel - the Arellano Felix organisation - in January 2008, sparking further violence.
He allied himself with Joaquin "Shorty" Guzman, head of the rival Sinaloa cartel and top of Mexico's most-wanted list.
The country's president, Felipe Calderon, has made a war on drug traffickers his political priority.
But, since he took office in 2006, more than 15,000 people have died in spiralling drug violence, above all in border regions which control the lucrative access routes into the US market.