A police tactical team prepares to enter a home in the 100 block of Dade Avenue in Ferguson, Missouri, on as they search for a gunman who shot two police officers during a protest Thursday.

Police mobilize in the parking lot of the Ferguson Police Station after two police officers were shot.

A protester yells at police outside the police department in Ferguson, Mo.

Police shine a light on and photograph a helmet as they investigate the scene where two police officers were shot outside the police department Thursday in Ferguson, Mo. The Associated Press

Police take cover after two officers were shot while standing guard in front of the Ferguson Police Station on Thursday. The Associated Press

Police mobilize in the parking lot of the Ferguson Police Station after two police officers were shot while standing guard in front of the station on Thursday. The Associated Press

Police stand watch outside the Ferguson Police Department where two police officers were shot early Thursday.

Police and protesters square off outside the Ferguson Police Department Wednesday. Earlier in the day, the resignation of Ferguson police chief Thomas Jackson was announced in the wake of a scathing Justice Department report prompted by the fatal shooting of an unarmed black 18-year-old by a white police officer.

A police helmet, splatter with what appears to be blood, sits on the ground outside the Ferguson Police Department.