By some accounts, the Kaibiles could be considered more dangerous than the Zetas, whose training in the Mexican armed forces was primarily for anti-drug operations. "Their preparation is different," Ibarrola said of the Kaibiles. "Their intentions are different: simply to kill."

Other analysts agreed. "The Kaibiles were always an elite force whose primary mission was to conduct massacres," said analyst Carmen Aida Ibarra of Guatemala's Fundacion Myrna Mack. "But this is the first clear confirmation that they are being co-opted by the drug traffickers."

More here, here and here

The U.S. embassy in Guatemala released a statement last year:

“The presence of U.S. officers forms part of a training commitment in response to an invitation from the Guatemalan Army, which training is carried out continuously, in association with military and police forces, by means of a diplomatic agreement” between the two nations.

“Guatemalan military and police personnel are trained by their U.S. counterparts in operations to control illicit trafficking by land, sea, and air,” the diplomatic mission added.

The cables released by Wikileaks are illuminating. Here's one from 2009:

What is happening there is typical of many rural areas of Guatemala. Sources tell us that Coban's police are corrupt and allied with traffickers, and sometimes even provide them escort. Some judges and prosecutors are
too frightened to do their jobs properly; others are in league with the traffickers.

The Economist blames U.S. drug policy. The fundamental problem:

As long as drugs that people want to consume are prohibited, and therefore provided by criminals, driving the trade out of one bloodstained area will only push it into some other godforsaken place. But unless and until drugs are legalised, that is the best Central America can hope to do.

Also see, Why Mexico's War on Drugs is Unwinnable.

And 2012 U.S. aid budget numbers (at page 125) for the drug war: Mexico, 248 million, Colombia, 160.5 million, Central America Regional Security Initiative (CARSI) ($55 million),Caribbean Basin Security Initiative (CBSI) ($30 million).

Add that to the global numbers which include things like International Law Enforcement Academy (ILEA) ($31.3 million) and Inter-regional Aviation Support ($60.7 million).

And compare to this: Demand Reduction ($12.8 million).