Army troops captured another suspect in the Oct. 3 murder of the son of former Coahuila state Gov. Humberto Moreira, Mexico's defense department said.

Carlos Arnulfo Flores was apprehended in Monclova, Coahuila, along with three associates who "assaulted the military personnel with gunshots," the department said in a statement.

Flores, reputed to be a local boss of the Los Zetas drug cartel, was treated for minor injuries received during the exchange of fire.

At least four other people were already in custody for the murder of former Gov. Moreira's son, which authorities say was an act of revenge for the death at police hands of the nephew of a top Zetas leader.

Jose Eduardo Moreira Rodriguez, 25, a regional coordinator of social development programs for the Coahuila state government, was slain near the Mexico-U.S. border just hours after police killed Miguel Angel Treviño Morales' nephew.

"The order was given to kill a nephew of the governor ... and it was my son they killed," Humberto Moreira said last week, relaying what prosecutors had told him.

Ruben Moreira, Humberto's brother, is the current governor of Coahuila.

Poet Javier Sicilia, who launched a campaign against the Mexican government's military-oriented drug strategy after his own son was slain in 2010, wrote Humberto Moreira a letter of condolence on the death of Jose Eduardo.

"He and I had the opportunity, unfortunately, to bury our sons, but there are thousands of families who have never even seen their sons again, because they are missing," Moreira told Radio Formula last week.

More than 60,000 people have died in Mexico's drug war over the last six years. EFE