Federal authorities said Wednesday they had arrested an Iraqi citizen and longtime member of Al Qaeda and the Islamic State who fled after killing an Iraqi police officer in 2014, eventually settling in Sacramento as a purported refugee.

The man, Omar Ameen, 45, is wanted on a murder charge in Iraq and appeared before a federal magistrate judge in Sacramento on Wednesday soon after his arrest, the Justice Department said in a statement. He is to be extradited and will face trial in his home country, prosecutors said.

Mr. Ameen has been a member of Al Qaeda in Iraq since at least 2004 and later joined the Islamic State — known as ISIS — prosecutors said, citing interviews with several witnesses. He is not known to have renounced his membership in either group, they say.

“It is common knowledge in Rawah, Iraq, that Ameen was a main local figure of AQI and ISIS,” a detention memorandum said.