GARDEZ, Afghanistan -- Mohammed Naim Farouq was a thug in the lawless Zormat district of eastern Afghanistan. He ran a kidnapping and extortion racket, and he controlled his turf with a band of gunmen who rode around in trucks with AK-47 rifles.

U.S. troops detained him in 2002, although he had no clear ties to the Taliban or al Qaeda. By the time Farouq was released from Guantánamo the next year, however — after more than 12 months of what he described as abuse and humiliation at the hands of American soldiers — he'd made connections to high-level militants.

In fact, he'd become a Taliban leader. When the U.S. Defense Intelligence Agency released a stack of 20 "most wanted" playing cards in 2006 identifying militants in Afghanistan and Pakistan — with Osama bin Laden at the top — Farouq was 16 cards into the deck.

A McClatchy investigation found that instead of confining terrorists, Guantánamo often produced more of them by rounding up common criminals, conscripts, low-level foot soldiers and men with no allegiance to radical Islam — thus inspiring a deep hatred of the United States in them — and then housing them in cells next to radical Islamists.

The radicals were quick to exploit the flaws in the U.S. detention system.

Soldiers, guards or interrogators at the U.S. bases at Bagram or Kandahar in Afghanistan had abused many of the detainees, and they arrived at Guantánamo enraged at America.

The Taliban and al Qaeda leaders in the cells around them were ready to preach their firebrand interpretation of Islam and the need to wage jihad, Islamic holy war, against the West. Guantánamo became a school for jihad, complete with a council of elders who issued fatwas, binding religious instructions, to the other detainees.

Rear Adm. Mark H. Buzby, until recently the commanding officer at Guantánamo, acknowledged that senior militant leaders gained influence and control in his prison.

"We have that full range of (Taliban and al Qaeda) leadership here, why would they not continue to be functional as an organization?" he said in a telephone interview. "I must make the assumption that there's a fully functional al Qaeda cell here at Guantánamo."

Afghan and Pakistani officials also said they were aware that Guantánamo was churning out new militant leaders.

In a classified 2005 review of 35 detainees released from Guantánamo, Pakistani police intelligence concluded that the men — the majority of whom had been subjected to "severe mental and physical torture," according to the report — had "extreme feelings of resentment and hatred against USA."

The report warned that unless steps were taken to rehabilitate the men, they had the potential of "becoming another Abdullah Mehsud," a former Guantánamo detainee who became a high-ranking Taliban commander in the Pakistani tribal areas bordering Afghanistan. Mehsud killed himself with a grenade last July to avoid being taken prisoner by Pakistani troops.

"A lot of our friends are working against the Americans now, because if you torture someone without any reason, what do you expect?" Issa Khan, a Pakistani former detainee, said in an interview in Islamabad. "Many people who were in Guantánamo are now working with the Taliban."

According to Afghan authorities, Mohammed Naim Farouq was a rural gangster, not a terrorist.