WEST POINT, Neb. (AP) – A mistrial has been declared in a northeast Nebraska murder case.

Cuming County jurors had heard nine days of testimony regarding the second-degree murder and other charges against Derek Olson before the mistrial was declared Tuesday. Prosecutors say Olson and his father, Jody Olson, killed 64-year-old Ernest Warnock on March 10, 2017, at Warnock’s home in Rosalie.

The judge said the mistrial was warranted because a former Nebraska State Patrol investigator mentioned a lie detector test taken by Jody Olson. The judge says Jody Olson’s testimony is key, so it’s important that jurors not be swayed by the fact that a witness took and may have passed a test.

Jody Olson pleaded guilty to a charge of second-degree murder and agreed to testify against his son as part of a plea deal.

Derek Olson’s second trial is scheduled to begin May 6.