cnn.com – Your video will begin momentarily. (CNN) — Ahead of a grand jury’s decision on whether to indict a police officer in the killing of Michael Brown, Missouri has both called in the National Guard and diminished the role of the Ferguson Police Department. Missouri Gov. Jay Nixon declared a state of emergency Monday as a precaution, he said, in the event of unrest or violence. It’s unknown when the grand jury will hand down a decision on whether to indict Ferguson Police Officer Darren Wilson for his fatal shooting of Brown, a teen.