A special prosecutor says a grand jury has been impaneled to hear evidence into a possible cover-up by Chicago police officers in the fatal shooting of Laquan McDonald.

Patricia Brown Holmes on Wednesday told Chief Criminal Court Judge LeRoy K. Martin Jr. the special grand jury will begin issuing subpoenas over the next 30 to 45 days. She did not say if the jurors have already heard any evidence.

Martin named Holmes to look into whether officers lied to justify the October 2014 shooting of the 17-year-old McDonald.

Video released last year showed officer Jason Van Dyke shooting McDonald 16 times. Van Dyke has pleaded not guilty to murder.

No other officers have been charged in the incident that prompted numerous protests after video of the shooting was made public.