TULSA, Okla. (AP) — A former police officer facing a fourth trial for the death of his daughter's black boyfriend can't be tried in Oklahoma because the shooting happened on American Indian territory, his attorneys argued in a new court filing.

Citing his membership in the Muscogee (Creek) Nation, attorneys for ex-Tulsa Police Department Officer Shannon Kepler asked a judge Friday to dismiss the case because the 2014 shooting happened on land inside tribal territory. The Tulsa World reported that Kepler was issued a Creek Nation citizenship identification card on Thursday.

Kepler's attorneys also cited a Tuesday decision by the 10th U.S. Circuit Court of Appeals that overturned the first-degree murder conviction and death sentence of Oklahoma inmate Patrick Dwayne Murphy. He asserted that state courts lacked jurisdiction because he was a member of the Creek Nation and that the crime occurred on Indian territory.

The federal appeals court concluded that decisions about the borders of the Creek reservation remained with Congress.

Kepler is charged in the August 2014 fatal shooting of 19-year-old Jeremey Lake. Kepler doesn't deny shooting Lake, but told investigators he acted in self-defense because he thought Lake was armed. Police found no weapon on Lake or at the scene.

Three mistrials in less than a year have been declared in Kepler's case. In the most recent trial, jurors deadlocked 6-6 last month after almost three hours of deliberations. Juries in Kepler's previous two trials, in November and February, deadlocked 11-1 and 10-2 in favor of guilt before a judge declared mistrials after up to 12 hours of deliberations in each case.

Kepler's fourth trial begins Oct. 9