FILE - In this April 20, 2017, file photo, Chicago police officer Jason Van Dyke, who is charged in the 2014 shooting death of black teenager Laquan McDonald, appears at a hearing in his case at the Leighton Criminal Courts Building in Chicago. Judge Vincent Gaughan on Thursday Sept. 17, 2017, ruled that statements Van Dyke made to an investigator two days after he fatally shot a black teenager in 2014 cannot be used at his murder trial. Gaughan sealed an audio recording and a transcript of an interview that Van Dyke gave to the agency that investigates police shootings in Chicago . (Nancy Stone/Chicago Tribune via AP, Pool, File)

CHICAGO - A judge on Thursday ruled that statements a white Chicago police officer made to an investigator two days after he fatally shot a black teenager in 2014 cannot be used at his murder trial.

During a brief hearing, Cook County Judge Vincent Gaughan sealed an audio recording and a transcript of an interview that Officer Jason Van Dyke gave to the agency that investigates police shootings in Chicago after Van Dyke shot 17-year-old Laquan McDonald. Gaughan's ruling means that the material cannot be released publicly or used by prosecutors against Van Dyke because he was required to talk to the Independent Police Review Authority. A legal rule prohibits statements officers are required to give from being used against them if they are charged with a crime.

Gaughan also ordered sealed statements that former Deputy Chief David McNaughton made to the city's inspector general's office. That material also cannot be used a trial or released to the public.

Police dashcam video shows that Van Dyke shot McDonald 16 times as the teen was walking away from officers with a small knife by his side. Van Dyke has pleaded not guilty to first-degree murder, and three other officers have pleaded not guilty to conspiring to cover up what happened.

Gaughan is trying to navigate a case that has raised a host of complicated legal issues about what evidence prosecutors can use and in some cases what they can see. Attorneys have been arguing for months about the statements that Van Dyke and other officers at the scene of the shooting made. McNaughton was the highest ranking member of the Chicago Police Department at the scene.

Special prosecutors were not even allowed to attend the portion of Thursday's hearing in which Van Dyke's statements and McNaughton's statements were discussed. Instead, Gaughan made his ruling to attorneys whose job it is to examine what evidence the special prosecutors can have at their disposal.

Gaughan previously ruled that statements Van Dyke made to a detective can be used by prosecutors, as can statements he made to police union representatives. But the judge has ruled that prosecutors cannot use statements he made to McNaughton, who determined that Van Dyke acted properly and who retired last year after the inspector general's office recommended he be fired.

News from © The Associated Press, 2017