Officer Krystal Rivera was excited to celebrate her daughter's 11th birthday this weekend. But Rivera's life was tragically cut short late Thursday, when she was fatally shot in the back by a bullet fired by another officer.

Chicago police officials say an officer killed this week was accidentally shot and killed by her partner after they encountered someone with a rifle when they chased a suspect into an apartment.

Chicago police Officer Krystal Rivera was mistakenly shot and killed by a fellow cop during a confrontation with an armed suspect late Thursday, according to police, who continue to hold at least