A Chicago police officer was unintentionally shot and killed by her partner after they chased a suspect into an apartment and encountered another person with a rifle, officials said. Krystal Rivera, 36,

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.

"That officer is in a very, very tough place; unimaginable what that officer has to be feeling right now," Chicago Police Supt. Larry Snelling said.