Soldiers detained Edgar Jimenez late Thursday at an airport outside Cuernavaca, 50 miles south of Mexico City, as he prepared to board a flight to Tijuana. Officials said he was accompanied by a sister and was heading to his native San Diego, where his mother lives.

Presented to the news media Friday morning, Jimenez said he had beheaded at least four adversaries of the so-called South Pacific Cartel, a remnant of the Beltran Leyva crime syndicate. The small, mop-haired boy known as El Ponchis, or "The Stoner," said he committed the killings while stoned on marijuana and at the orders of the gang boss in command of the Cuernavaca area. Authorities said he was caught with two cell phones that held photographs of tortured victims.

"I didn't know what I was doing," Jimenez said, according to media accounts, but added that he was paid $2,500 per killing. Army officials accused Jimenez's sister, identified as 19-year-old Elizabeth, of also working for the gang. Neither has been formerly charged.

Jimenez said he was sorry to have gotten involved both with Mexican gangsters and with killing people. If he beats the charges, he said, he'll change his ways.

"I didn't join," he said of his gangland career, which reportedly began when he was 12. "They pulled me in."

Security forces had been looking for Jimenez since he appeared last month along with other teens in YouTube videos, brandishing weapons and bragging of their gangland exploits.

Mexican officials say he is a U.S. citizen, and American officials are trying to confirm his nationality.

Wouldn't be the first

If he is, indeed, proved to have committed killings, Jimenez will hardly be the first U.S. teenager involved in the Mexican gangs.

Several Laredo teenagers were convicted in 2007 for carrying out killings on behalf of the Zetas, the violent organization entrenched in Nuevo Laredo and other towns along the South Texas border.

One of those teens, Rosalio "Bart" Reta, killed his first victim at age 13 and might have murdered more than 30 others before being captured. Reta was convicted and is now serving a 70-year sentence in a Texas state prison.

Once among Mexico's most powerful gangs, the Beltran Leyva organization has fallen into brutal internecine war since Mexican marines killed kingpin Arturo Beltran Leyva last December.

The slain drug lord's underlings — including Laredo native Edgar Valdez Villarreal, also known as La Barbie - quickly began fighting with one another to replace him.

Their feuding has killed hundreds of people this year in and near Cuernavaca and throughout neighboring Mexico and Guerrero states, including the beach resort of Acapulco.

Many of the those killed have been beheaded, which in the past four years has become an nauseatingly banal terror tactic of the gangsters.

Among the victims were more than 50 men thrown down a 500-foot abandoned mine shaft outside the colonial tourist town of Taxco, and 20 Mexican tourists massacred together in Acapulco, apparently in a case of mistaken identity.

Fallout from WikiLeaks

Valdez was captured in August in a Mexico City suburb and awaits extradition to the United States. Several of his top lieutenants have been captured, as well.

The arrest of the alleged boy beheader came as Mexican and U.S. officials scrambled to contain damage caused by diplomatic cables leaked Thursday that reveal deep worries about Mexico's conduct of a four-year crackdown on organized crime.

The campaign, which has heavily relied on the military, has led to some 30,000 deaths. Most of those killings have been in assassinations or shootouts between gangsters rather than in battles between troops and thugs.

Mexico 'fully in control'

Cables from the U.S. Embassy in Mexico City, filtered Thursday to European papers by WikiLeaks, include criticism of the army's performance and reports of Mexican officials' fears that the government had lost control of areas of the country.

American Ambassador Carlos Pascual issued a statement on Friday condemning WikiLeaks and assuring Mexicans that the U.S. commitment to their country remains strong.

"Cable reports do not represent U.S. policy," Pascual wrote. "They are often impressionistic snapshots of a moment in time. But like some snapshots, they can be out of focus or unflattering."

On Friday, the Mexican government's spokesman for security matters denied that officials have ever believed or feared that they'd lost control in parts of the country.

The situation across Mexico "demonstrates that the Mexican government is fully in control of territory," spokesman Alejandro Poire said.

Poire added, however, that Mexican officials "share the public's concern about criminality that affects, in particular, some areas of the country."

dudley.althaus@chron.com