ARLINGTON, Va. — The Ethiopian jail guard suspected of torturing and maiming political prisoners during that country’s ‘‘Red Terror’’ era came to the United States in 2004 under a false identity, seeking asylum and claiming he would be persecuted if he returned home.
He lived comfortably in Denver until 2011, when another Ethiopian who recognized him outside a cafe confronted him with the words ‘‘I think I know you.’’
That’s how Kefelegn Alemu Worku, convicted last year of identity theft and immigration fraud, came to the attention of federal authorities.
The government would like to see that happen more often.
A Justice Department lawyer recounted Worku’s case at a presentation for refugee advocates, part of an outreach to encourage the reporting of human-rights abusers hiding in plain sight. The hope is to raise the profile of a relatively new prosecution unit and to make refugees comfortable with helping investigators — a major challenge in human-rights criminal cases.
Part of preventing atrocities ‘‘is accountability for what people have done,’’ said Teresa McHenry, chief of the department’s Human Rights and Special Prosecutions section.
The cases are challenging, costly, and not always successful. Prosecutors must reconstruct crime scenes from other countries that are sometimes decades old. Witnesses may be scattered across the globe.
Advocates say they wish prosecutors would bring more cases. Defense lawyers criticize the Justice Department for prosecuting their clients when others may be equally culpable and for using testimony they argue is not always credible.
‘‘There’s a whole layer of doubt in the reliability of witnesses who now, 20 years later, talk about this stuff,’’ said Mark Howard, who defended a woman convicted of fraudulently obtaining US citizenship by lying about her role in the 1994 Rwandan genocide.
He said he was troubled when prosecutors in New Hampshire brought in new witnesses and appeared to change their legal theory at the retrial at which his client, Beatrice Munyenyezi, was found guilty.
‘‘Twenty years of cultural change and cultural education about the genocide has influenced what they say,’’ he said.
The Human Rights and Special Prosecutions Section was formed in 2010 from two units, including one that specialized in hunting down Nazi criminals. But as that population has dwindled, concerns have grown about refugees who lie on visa or asylum applications to enter the United States.
In 2011, President Obama called preventing mass atrocities a ‘‘core national security interest’’ and expanded the grounds on which immigrants could be denied entry, including involvement in slavery.
Immigration and Customs Enforcement created a war crimes center five years ago. And new or amended laws have expanded the Justice Department’s reach.
Congress in recent years has expanded the genocide statute to permit prosecution of defendants who are in the United States and outlawed the recruitment of child soldiers. Prosecutors say they hope to take more advantage of those tools but generally bring immigration-related charges in cases where the crime occurred before the statutes were changed.
The human rights section has secured convictions of, among others, a former Guatemalan officer who hid his role in a 1982 massacre and a Bosnian who concealed his affiliation with a brigade that committed atrocities on Muslims.