DETROIT -- A judge has denied a request to lower a $500,000 bail set for two parents who are charged with their son in a fatal Michigan school shooting.

Judge Julie Nicholson said James and Jennifer Crumbley failed to turn themselves in when they were charged with involuntary manslaughter on Dec. 3 and have few ties to the area.

The Crumbleys have been in jail since Dec. 4 and unable to post their bond. They are charged in a shooting that killed four students at Oxford High School on Nov. 30.

They're accused of making a gun accessible to their son, Ethan Crumbley, and failing to intervene on the day of the shooting when counselors revealed his distressing drawings of violence.

Ethan is charged as an adult with murder and other crimes. Earlier Friday, the 15-year-old waived his right to a key evidentiary hearing and moved his case to the trial court in Oakland County.