CHICAGO — The judge presiding over the case of a Chicago police officer charged in the shooting death of a black teenager cleared the courtroom for a hearing in the first-degree murder case.

Judge Vincent Gaughan said he was sealing Friday's hearing out of concern for the safety of witnesses.

The witnesses called by Officer Jason Van Dyke's defense team were to outline Laquan McDonald's troubled past. Van Dyke is charged in the 2014 shooting death of the 17-year-old.

Under Illinois law, attorneys can attempt to present evidence of a victim's violent character or history to prove the defendant acted in self-defense. Gaughan must decide how much of that testimony will be allowed.

Video show Van Dyke opened fire as McDonald walked away from police with a knife in his hand.