The 10 women and two men could not reach a unanimous verdict in their penalty deliberations Thursday after finding Cope guilty a day earlier.
He killed Sgt. Timothy Prunty on Oct. 24, 2010.
The jury decides whether Cope spends the rest of his life in prison or is executed.
The jury foreman told Judge Mike Pitman that no amount of deliberation was going to change deadlocked jurors’ minds.