Atlanta ? Many people on the street where Kathryn Johnston lived fortify their windows with metal bars and arm themselves for protection.

Johnston, 92, was no exception.

She was waiting with her gun on Tuesday night when a group of plainclothes officers with a warrant knocked down her door in a search for drugs, police said. She opened fire, wounding three officers, before being shot to death, police said.

Assistant Police Chief Alan Dreher called the killing “tragic and unfortunate” but said the officers were justified in returning fire. “You don’t know who’s in the house until you open that door,” he said Wednesday. “And once they forced open the door, they were immediately fired upon.”

The Rev. Markel Hutchins, a civil rights activist and spokesman for Johnston’s family, said he could understand why the elderly woman would arm herself. “She was afraid,” Hutchins said. “This is a horrifying situation in a neighborhood where crime happens often. This incident is a result of a mix-up.”

The officers had gone to the old woman’s house with a search warrant after buying drugs from a man there, police said. Dreher would not say how the dealer knew Johnston.

District Attorney Paul Howard said that his office is looking into the shooting but that a preliminary review indicates the officers had a right to search the home.