When the Americans invaded in October 2001, Khan was living in Kandahar City, selling kerosene and gasoline. On Nov. 13, 2002, he was riding his motorcycle from his home to the market when he was arrested by four Afghan men who work for the corrupt warlord Gul Agha Shirzai, who governed Kandahar province. A short while later, Khan was transferred to the Americans.

Khan was no doubt sold to the United States for a cash bounty. Shortly after the U.S. invasion, the U.S. military littered Afghanistan with leaflets offering bounties of up to $20,000 cash in exchange for the capture of al Qaeda or Taliban fighters. One leaflet promised: "Enough money to take care of your family, your village, your tribe for the rest of your life."

Most fifth-graders would understand that offering cash bounties to the people of one of the poorest and most corrupt countries on earth is unlikely to produce reliable information about terrorists. Nevertheless, in a November 2001 press briefing, Secretary of Defense Donald Rumsfeld bragged that the bounty leaflets were falling from the Afghan sky "like snowflakes." More than 90 percent of the Guantanamo detainees were captured by tribal warlords or groups such as the Northern Alliance before being turned over to the Americans.

Khan's confidential file reveals that, around the time of his capture, one or more Afghan informants told U.S. intelligence officials in Kandahar that Khan was an active member of a local insurgent group that was plotting to bomb Americans in and around the Kandahar region. The U.S. intelligence officer did not bother to record the informant's name or whether he was paid a bounty. Nor did he inquire how the informant acquired his information or whether the informant is a credible person or a criminal. Nor did the official attempt to corroborate the allegations against Khan before sending him off to the newly built prison at Guantanamo.

John Bates, a federal judge in Washington, D.C., has reviewed the confidential "evidence" against Khan and declared that all of the allegations against him come from reports containing "multiple levels of hearsay" and that "all of the information contained in the reports could come from a single individual" and that "no source is identified by name." Nevertheless, Khan remains at the Guantanamo Detention Center, along with 230 others. There can be no doubt that Khan, and many or most of his fellow detainees, were sent to Gitmo because U.S. intelligence officials accepted, without question, the unsubstantiated allegations of local warlords and bounty hunters.

During the six-plus years of his captivity, Khan has repeatedly told his interrogators that he is a poor shopkeeper from Kandahar, not a terrorist and not an enemy of the United States. The only other detainee at Guantanamo from the Kandahar region was shown Khan's photograph. He told his interrogators that Khan "was a shopkeeper who sold gasoline in Kandahar" and was not a terrorist.

Khan can never be tried in a court of law or even in a military tribunal because our government has no evidence against him. It can produce no witnesses, physical evidence, incriminating documents or confessions.

If President Obama goes forward with his plans for preventative detention, U.S. officials will be given the power to choose--either to admit their mistakes, which appear to be so negligent as to rise to the level of crimes, or to bury their mistakes forever under the cloak of national security. No government should be trusted with this kind of power.