From the March 31st Wall Street Journal (firewall, sorry):
When the Pentagon needed someone to prosecute a Guantanamo Bay prisoner linked to 9/11, it turned to Lt. Col. V. Stuart Couch. A Marine Corps pilot and veteran prosecutor, Col. Couch brought a personal connection to the job: His old Marine buddy, Michael “Rocks” Horrocks, was co-pilot on United 175, the second plane to strike the World Trade Center on Sept. 11, 2001.
The prisoner in question, Mohamedou Ould Slahi, had already been suspected of terrorist activity. After the attacks, he was fingered by a senior al Qaeda operative for helping assemble the so-called Hamburg cell, which included the hijacker who piloted United 175 into the South Tower. To Col. Couch, Mr. Slahi seemed a likely candidate for the death penalty. "Of the cases I had seen, he was the one with the most blood on his hands," Col. Couch says. But, nine months later, in what he calls the toughest decision of his military career, Col. Couch refused to proceed with the Slahi prosecution. The reason: He concluded that Mr. Slahi's incriminating statements - the core of the government's case - had been taken through torture, rendering them inadmissible under U.S. and international law. The Slahi case marks a rare instance of a military prosecutor refusing to bring charges because he thought evidence was tainted by torture. For Col. Couch, it also represented a wrenching personal challenge. Laid out starkly before him was a collision between the government's objectives and his moral compass.