A trial witness has identified an Ethiopian immigrant living in Colorado as a prison guard who tortured and killed inmates in the African nation in the late 1970s.

The testimony came in Denver federal court on Thursday in the trial of Kefelgn Alemu Worku on charges of unlawfully procuring citizenship or naturalization and identity theft. Prosecutors claim he lied on immigration forms when he denied committing political persecution.

If convicted, he could face up to 12 years in prison and a fine of up to $500,000. He has not been charged in Denver with any crimes related to prison abuse.

Worku has acknowledged using a false name to gain admission to the U.S. but denies the torture allegations.

Abebech Demissie, a naturalized U.S. citizen from Ethiopia, testified that she was an inmate at the prison known as Higher 15 in Addis Ababa in the late 1970s and saw Worku shoot and kill two other inmates, both teenage boys, The Denver Post reported (http://tinyurl.com/m5bxre9).

Demissie said Worku and other guards tied her up and beat her.

Worku’s attorney, Matthew Golla, questioned whether Demissie could accurately identify Worku more than 30 years after the events at the Ethiopian prison.

“I can’t delete what I have in my memory,” she replied.

Worku came to the United States in 2004 and had been living in Denver

Authorities say a former prisoner at Higher 15 recognized Worku at a suburban Denver restaurant in 2011 and alerted law enforcement officers.

Higher 15 was established amid a campaign known as Red Terror. Human Rights Watch, a watchdog group, called it “one of the most systematic uses of mass murder by a state ever witnessed in Africa.”

Golla said Worku has lived peacefully in Denver for eight years, working at Denver International Airport and for a parking lot company.