In a ruling on the technicalities of Lt. Ehren Watada's first trial, U.S. District Judge Ben Settle said prosecuting Watada again would amount to double jeopardy.
Watada's first trial in 2007 ended in a mistrial when the presiding military judge ruled Watada had not fully understood a stipulation he had signed.
What happens next is unclear, the Seattle Post-Intelligencer said Wednesday. The Army will have to decide whether to resurrect charges of conduct unbecoming an officer involving interviews Watada gave after refusing to ship out with his Fort Lewis unit in 2006.
The newspaper said prosecutors had dropped the specifications earlier.
Watada became a headliner for the anti-war movement when he refused to deploy and called the U.S. war in Iraq illegal.