Figures released by the Attorney General's office in response to a freedom of information request by the Associated Press, show 23 senior and mid-level Zetas bosses were arrested and another four killed since last December. They include uber-capo Miguel Angel Treviño, Z40, who was arrested by Mexican marines near the South Texas border in July.

The Zetas are among 69 gang bosses who officials say have been taken down since Peña took office last December. Officials refuse to name the remaining 53 gangsters on a list of 122 drawn up by Peña's security officials, saying they don't want to alert the gangsters they're being targeted.

The second most battered group was the previously unknown Western Cartel, which officials say operations in the La Laguna area of Durango and Coahuila states and had 17 bosses arrested.
Just seven underbosses were captured and two killed from the Sinaloa Cartel, nominally headed by Joaquin "El Chapo" Guzman and considered Mexico's most powerful.

But last Thursday's release of names of killed or captured gang bosses came a day after Mexican marines reportedly killed Gonzalo Inzunza, 42, a top lieutenant of Sinaloa kingpin Ismael "El Mayo" Zambada in a firefight in Puerto Peñasco, a beach resort about 50 miles below the Arizona border that's popular with Americans.

Known as "El Macho Prieto," Inzunza was a top Sinaloa Federation assassin who in recent years had headed the gangs operations in Sonora and Baja California. Although the Navy says he is dead, Inzunza's body remains missing, reportedly carried away by his gunmen following a firefight that left five other men dead in the street.

Inzunza was also reportedly the target of an ill-fated United States' Bureau Alcohol, Tobacco and Firearms (ATF) investigation along the Arizona - Mexico border. The so-called "Fast and Furious" operation monitored guns purchased in the US as they "walked" across the border into cartel hands.

One of those weapons was recovered after a shootout between border agents and suspected Mexican criminals in which a US border agent was killed. Hundreds more have been recovered in Mexico crime scenes. Macho Prieto's operations proceeded unimpeded. 

InSight Crime Analysis

In sharp contrast to policy under former President Felipe Calderon, Mexican officials this year have downplayed the importance of detained or fallen gangsters, offering scant details of their roles. Officials argue that the "perp walks" before network news cameras favored under Calderon only served to glorify the gangsters in the eyes of impressionable youths.

Maybe so. But the forced release of the list of killed and captured capos shows that the Peña government has continued with the US-backed "kingpin strategy" favored by Calderon. And the relative disintegration of the Zetas as a national threat suggests the strategy can bear fruit if officials keep their shoulders to the wheel.

Analysts have argued in the past that taking down the gangs' leadership enhances violence the short term, as rivals within the organization fight to take the top spots and rivals move in on trafficking routes and other vice rackets.

That happens. But if second and third tier bosses are targeted as well, a gang's operational capacity might be gutted.

The Zetas have been heavily targeted by the government since 2010, when their feud with former paymasters in the Gulf Cartel turned Monterrey and much of northeastern Mexico into one of the country's bloodier corners.

The Zetas became a special project of the Mexican navy, whose commandos were the security forces' most trusted and favored by Washington until this year.

Blamed for many of the more horrific massacres of recent years, including the murder of 72 Central American migrants and the dumping of 49 dismembered bodies outside Monterrey, the Zetas simply became too vicious to ignore.

The 2011 killing by a Zetas cell of a US federal agent in a highway ambush brought added heat on the gang. That the Zetas also hold sway in the sparsely populated borderlands that include the shale gas fields the government intends to develop in the coming years made their destruction still more urgent.

Jesus "El Mamito" Rejon, then the Zetas third ranking boss, was captured in July 2011 during the push to bring down the US agents' killers. Marines killed Heriberto Lazcano, who headed the Zetas along with Treviño, in October 2012.

The government announced last week that murders this have declined by 15 percent overall, compared to 2012, and attributed much of the drop to a quieting in the Zetas lands of northeastern Mexico. The feared explosion of violence in the Zetas stronghold of Nuevo Laredo and elsewhere following Treviño's arrest has yet to happen.

But Zetas aside, the released list of de-activated capos also underscores the frustrating "whack a mole" reality of the campaign against the cartels.

After a cartel's bosses and underbosses are taken down, smaller cells simply form new alliances, narcotics and human trafficking continues apace. The extortion, kidnappings and assaults most threatening to ordinary Mexicans grows.

The PGR report delivered to the AP identifies 12 distinct criminal gangs operating across Mexico. The gangs include a previously unheard of "Western Cartel" operating in Coahuila and Durango.

Coahuila has been considered the fief of the Zetas and Durango of the Sinaloa Federation. Fighting between those groups, and between Sinaloa factions have killed hundreds, if not thousands of people in recent years in Torreon and neighboring Gomez Palacios, as well as Durango City, capital of the state.

The Western Cartel -- a bland name probably coined by officials rather than gangsters -- seems comprised mostly of remnants of the gang controlled by Sergio Villarreal, alias "El Grande," a lieutenant of the Beltran Leyva Organization (BLO), which broke with the Sinaloa Federation five years ago.

Villarreal warred with Edgar Valdez, alias "La Barbie," for control of the organization following the killing by Mexican marines of kingpin Arturo Beltran Leyva four years ago. Both men were arrested in 2010 and Villarreal was extradited to the United States.

Those identified as the Western Cartel's leaders were arrested in March amid Sinaloa's struggle with the Zetas for control the cities of Gomez Palacios and Torreon. At the time of the arrests the gang was called the Cartel of La Laguna. 

As the Zetas have unraveled, the Gulf and Sinaloa Cartels have regained criminal dominance in Monterrey. Sinaloa also has gained dominance in Juarez, where killings tallied this year are about 15 percent of those in 2010, when the gang war for the city peaked.

Apart from the nationwide decline in murders -- which outside analysts dispute -- there is no indication the narcotics trade or other criminal activities have been affected by the arrests of the gangland bosses.