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 (AP) — 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, a four-year veteran of the department, is survived by a 10-year-old daughter.

The partner was the only person who fired a weapon, and the “gunfire unintentionally struck Officer Rivera,” city police said in a statement Friday. An autopsy showed she was shot in the back.