A grand jury could start hearing evidence Wednesday in the shooting death of 18-year-old Michael Brown.
St. Louis County Prosecuting Attorney Bob McCulloch is overseeing the case that will determine whether Ferguson police officer Darren Wilson faces criminal charges for the Aug. 9 shooting.
McCulloch spokesman Ed Magee said prosecutors would try to start presenting evidence Wednesday, the regular once-a-week meeting date for the grand jury.
Cases often are presented to grand jurors in a single day, but Magee says this case is complicated and will take longer.
Brown's death has sparked violent clashes between police and protesters who want the officer to be charged.
Meanwhile, police in Ferguson are enforcing an order against static assembly.
Officers have been seen urging people to keep moving and avoid standing in one place. Journalists who gathered by midday at a burned-out convenience were also being dispersed.
Officers say the order is not meant to stop the protesters but to keep people moving.
Officers say the order came from the Missouri State Highway Patrol, which has assumed command of crowd-control measures since the killing of Michael Brown sparked days of protests in the city.
A state of emergency has been in place since Saturday.