A man suspected of being the No. 3 leader of the Los Zetas drug cartel was captured by army troops in northeastern Mexico, the Defense Secretariat said Thursday.

Carlos Oliva Castillo, who was in charge of the cartel's operations in Nuevo Leon, Coahuila and Tamaulipas, was arrested on Wednesday, the secretariat said.

The 37-year-old Oliva Castillo was detained in Saltillo, the capital of Coahuila state.

Oliva Castillo was "one of the most important leaders" of the cartel, ranking just below top boss Heriberto Lazcano Lazcano, alias "El Lazca," and Miguel Angel Treviño Morales, alias "El 40," the secretariat said.

He is suspected of ordering the torching of Monterrey's Casino Royale, where 52 people died on Aug. 25, the secretariat said.

Oliva Castillo was found at a house in Saltillo and captured without any shots being fired.

Los Zetas gunmen in the area, however, engaged army troops in a firefight in an effort to rescue the cartel boss.

The gunmen "tried to draw the Mexican army troops to other areas by staging attacks on the security forces in different parts of the city of Saltillo to try to mount a possible rescue, an action that failed," the secretariat said.

Oliva Castillo, who also used the alias Nazario Mendoza Velazquez, was turned over to the Attorney General's Office "without suffering any harm and respecting his human rights," the secretariat said.

Juan Carlos Garza Rodriguez, suspected of being the head of the Zetas leader's security detail, and Iracema Lopez Garza, who is believed to be Oliva Castillo's girlfriend, were also arrested in the operation.

Soldiers seized two rifles, two handguns, five kilos of marijuana, two vehicles, including one outfitted with armor, communications gear and computers from the suspects.

Oliva Castillo began his criminal career in 2005 in Tamaulipas, the birthplace of Los Zetas, a criminal organization that started out as the armed wing of the Gulf cartel, investigators said.

Los Zetas and the Gulf cartel ended their ties in March 2010 and are now at war in several states.

Oliva Castillo worked in 2009 as the accountant for the Zetas cell run by Eulalio Juarez Cifuentes, the gang's erstwhile boss in the northern state of Nuevo Leon.

He took over Juarez Cifuentes's operation in early 2010 and ran it until April 2011, when he handed over control of the business in Nuevo Leon to Francisco Medina Mejia, who ended up in command of the war that Los Zetas is waging against the Gulf cartel in the state.

"Oliva Castillo was currently in charge of moving drugs through the northeastern region of Mexico, which includes the states of Tamaulipas, Nuevo Leon and Coahuila," the cartel's bastions, the secretariat said.

He moved his operations center to Saltillo, a city with a lower level of violence, because of the intensity of the war between Los Zetas and the Gulf cartel, the Defense Secretariat said.

Oliva Castillo ordered Medina Mejia to attack the Casino Royale, the secretariat said.

Soldiers seized four firearms, 40 ammunition clips, 583 rounds of ammunition and four vehicles after the firefight in Saltillo.

Los Zetas, considered Mexico's most violent drug cartel, has been blamed for several massacres in recent years.

The cartel has been accused of being behind the Aug. 23, 2010, massacre of 72 migrants, the majority of them from Latin America, at a ranch outside San Fernando, a city in Tamaulipas.

The cartel has also been blamed for the massacre of 27 peasants in May at a ranch in Guatemala's Peten province, which borders Mexico and Belize.