OKLAHOMA CITY (AP) — An Oklahoma appeals court on Thursday overturned the manslaughter conviction and 15-year prison sentence of a former police officer based on a U.S. Supreme Court ruling that found that much of the eastern part of the state remains an American Indian reservation.

Former Tulsa officer Shannon James Kepler, 60, is a member of Creek Nation who was convicted of killing his daughter's boyfriend in Tulsa on land within the historic reservation of the Muscogee (Creek) Nation.

In a ruling last year known as the McGirt decision, the U.S. Supreme Court found that Oklahoma lacks juris...