Union members stood on the steps of City Hall Thursday to denounce the indictment against Sergeant Hugh Barry.
He is charged with second-degree murder in the death of Deborah Danner inside her home in the Castle Hill section last October.
Danner has a history of mental illness and was shot while charging at Barry with a baseball bat in her apartment.
The union says Barry was protecting himself.
Barry and other officers had managed to convince the woman to drop a pair of scissors she was holding. When she grabbed a wooden bat and ran at Barry, he fired.
Barry was carrying a Taser but fired his service weapon instead.
If convicted on the top charge, Barry could face life in prison.