One curious feature has emerged in the Mexican government’s four-year-old offensive against the country’s murderous drug cartels. Some trafficking organizations seem to be in the crosshairs of the authorities more than others. One gang in particular appears to have suffered far less damage than any of its competitors. David Shirk, the director of the University of San Diego’s Trans-Border Institute, notes that the Mexican government has delivered significant blows over the past few years to seven of the country’s eight most prominent cartels. Shirk speculates that the eighth, largely unscathed group, the Sinaloa cartel, might now become utterly dominant, especially in western and northwestern Mexico. If that occurs, he believes that it might actually prove beneficial by reducing the bloody power struggles that have so convulsed the country.

Since the beginning of 2009, the Beltrán-Leyva cartel seems to be the government’s primary target – by a wide margin. But we’ve seen that pattern of focusing on a single gang or a small number of gangs before. In the late 1990s and the early 2000s, federal authorities directed most of their efforts against the Arellano-Félix organization in Tijuana and weakened that once-powerful organization badly. The interesting question is why officials seem to zero-in on one gang of traffickers, while devoting less attention – sometimes much less attention – to certain competitors. In the late 1990s, the reason for that disparity was simple: Mexico’s drug czar was on the payroll of a competing cartel.

It is uncertain whether similar corrupt motives are in play on this occasion. But whatever the reason, the damage to other cartels, and especially the recent devastation of the Beltrán-Leyva faction, has worked to the definite advantage of the Sinaloa cartel. That also was true of the earlier offensive against the Tijuana organization.

A May 2010 National Public Radio report highlights the extent to which the Sinaloa group has benefited from the disparate treatment. And the apparent reasons certainly should create a great deal of uneasiness. An investigative team headed by veteran correspondent John Burnett found “strong evidence of collusion between elements of the Mexican army and the Sinaloa cartel,” especially in Juárez, a major trafficking portal and the epicenter of the drug-related violence. That conclusion was based on dozens of interviews with current and former law enforcement officials, elected representatives, victims of violence, and outside experts.

Arrest statistics that NPR compiled reinforce suspicions about a government bias in favor of Sinaloa leader El Chapo Guzmán and his organization. Since December 2006, authorities have arrested several thousand mid-and high-level cartel members. The greatest percentage (44 percent) of those arrested come from the Gulf-Zeta operation, both when those factions were united and after their split in 2009. La Familia comes in second with 15 percent, followed by the Beltrán-Leyva group with 13 percent. The Sinaloa and Tijuana cartels follow with 12 percent each, and the damaged and fading Juárez cartel brings up the rear with a mere five percent.

The Sinaloa total stands out as strikingly low. Virtually every credible expert considers the Gulf and Sinaloa organizations the most powerful trafficking operations. Yet, the number of arrests of Sinaloa operatives is just a little more than one-fourth of Gulf-Zeta total. More members of the smaller Beltrán-Leyva gang have been arrested, and the now much smaller and weaker Tijuana remnant is in a virtual tie with the Sinaloa cartel. The disparity involving the Beltrán-Leyva cartel has undoubtedly grown since the NPR report, given the number of high-profile arrests of that group’s leaders in recent months. It is also a little unsettling that the Beltrán-Leyva faction had split off from the Sinaloa cartel, and that defection and resulting competition was especially threatening to Guzmán and his henchmen. Whether intentionally or not, the Mexican government’s near obsession with taking down the Beltrán-Leyva gang is benefiting the Sinaloa leadership and the cartel’s overall position in the drug trade.

Statistics involving arrests in Chihuahua, a key front-line state in the drug war, given the massive violence in Ciudad Juárez, produce an even greater cloud of suspicion. NPR studied police and military press releases announcing the apprehension of drug gang members between March 2008 and May 2010. Since the Juárez and Sinaloa cartels have been the primary combatants in the war to control the lucrative drug trade through Juárez, it would be reasonable to expect a similar number of arrests involving each faction. Yet nothing of the sort has occurred. Eighty-eight Juárez cartel members were taken into custody. The Sinaloa cartel? A paltry 16. That massive disparity reeks of government favoritism.

The government of President Felipe Calderón of course vehemently denies any softness toward the Sinaloa cartel. The administration is not about to admit that Guzmán may be more skillful than his rivals in bribing federal police and military officials. But the most benign interpretation of the huge disparity, both nationally and in Chihuahua, is that Calderón and his advisers have decided to go after either the most violent or the most vulnerable organizations, and that the Sinaloa cartel does not stand out in either category. The Zetas and La Familia are more appealing targets, given the first standard. The Tijuana, Juárez, and Beltrán-Leyva groups might be better targets based on the second standard. A less benign interpretation is that the Sinaloa cartel has the authorities in its pocket, just as some of its predecessors did in the 1980s and 1990s with previous administrations in Mexico City.

At a minimum, the Mexican government owes both its own people and Washington (which is funding much of the anti-drug campaign) an explanation about why such a disparity of treatment that benefits the Sinaloa cartel continues.