Executive Office for Immigration Review spokeswoman Kathryn Mattingly says Judge Elizabeth Hacker issued a written decision Monday in John Kalymon's case.
Kalymon was stripped of his U.S. citizenship in 2007.
He served in the Ukrainian Auxiliary Police. The U.S. Justice Department says Kalymon claimed to have shot and killed a Jew in 1942 when Jews were being removed from what is now Lviv, Ukraine.
But he later denied having done so.
Defense lawyer Elias Xenos says he hasn't seen Hacker's decision but is disappointed and assumes "an appeal will be likely."