BOSTON — A Rwandan-born Ohio man was arrested on Thursday on charges he engaged in a three-decade scheme to conceal his involvement in the African nation’s 1994 genocide to enter the United States as a refugee and ultimately gain U.S. citizenship.

Federal prosecutors in Boston said that for years, Eric Nshimiye, 52, hid the fact that he participated in the massacre by the hard-line Hutu regime of an estimated 800,000 ethnic Tutsis and moderate Hutus during three months of slaughter.

In fact, he participated in the killings including by striking victims on the head with a nail-studded club before hacking them to death with a machete, prosecutors alleged.

Years later, after settling in Ohio, Nshimiye sought to derail any investigation into his scheme by lying at the immigration fraud trial of a former classmate who prosecutors have accused of also participating in the atrocities.

“Our refuge and asylum laws exist to protect true victims of persecution — not the perpetrators,” Acting U.S. Attorney Joshua Levy of Massachusetts said in a statement.

Nshimiye was arrested in Ohio, where he has lived since 1995, and detained after an appearance in a federal court in Youngstown. His lawyer did not respond to a request for comment.

His arrest came four years after the 2019 trial conviction in Boston of Nshimiye’s former classmate Jean Leonard Teganya, who prosecutors said committed immigration fraud by concealing his involvement in the genocide when seeking asylum.

Prosecutors said that during the killings, both men were medical students in the southern Rwandan city of Butare and active in the political party that helped perpetrate the genocide.

According to charging documents, Nshimiye helped identify Tutsis among patients and staff at a hospital which became a site for atrocities, and was directly involved in murders and encouraging rapes.

He left Rwanda in mid-July 1994 and traveled to Kenya, where he lied to U.S. immigration officials to gain refugee status, prosecutors said. He became a U.S. citizen in 2003.

He was called as a defense witness at Teganya’s trial and gave false testimony to exculpate him, prosecutors said. Teganya was sentenced to eight years in prison.