The defense says it's not sure which witnesses and experts it will call in the federal trial of a white ex-police officer charged in the shooting death of a black South Carolina motorist.

Attorneys for Michael Slager say they won't know until after Slager's state murder trial in the 2015 shooting of 50-year-old Walter Scott, who was fleeing from a traffic stop.

Slager, a former North Charleston police officer, stands trial on the state charge next month.

In court documents filed Wednesday, attorneys say until that trial is over they won't know which witnesses they'll call in Slager's trial next year on federal charges of violating Scott's civil rights and other counts.

The shooting, caught on a cellphone video, reignited the national debate over treatment of blacks by white officers.