Kefelegn Alemu Worku entered his plea in federal court in Denver on Tuesday. A judge denied bail.
Worku is accused of using falsified documents to enter the United States and live in Denver under an assumed name.
Three former prisoners picked Worku out of a photo lineup and identified him as a guard at a prison in Ethiopia where they were held. Two said he beat them and the third said he witnessed Worku abusing others.
Worku has been charged with unlawfully procuring citizenship or naturalization and aggravated identity theft. If convicted of both, he faces up to 12 years in prison and fines of up to $500,000.
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