The encounter between Ms. Danner and the police lasted 15 to 20 minutes, in the close quarters of her seventh-floor apartment at 630 Pugsley Avenue, officials said. It began with 911 calls from neighbors who had heard Ms. Danner being “loud and disruptive” in the hallway, Wanda Perez-Maldonado, an assistant district attorney, said in court. It was not the first time the police had been called to her home.

Four officers and two paramedics arrived around 6 p.m. and Sergeant Barry arrived minutes later. The encounter ended with Sergeant Barry firing twice, fatally wounding Ms. Danner, who was in her bedroom.

The sergeant could face life in prison if convicted of the most serious charge.

Initially, the police said that Sergeant Barry persuaded Ms. Danner to drop a pair of scissors, but that she picked up a bat and tried to swing at him. Only Sergeant Barry was in the bedroom with Ms. Danner.

Sergeant Barry testified before the grand jury last week, said Mr. Quinn, who declined to provide details.

Image Deborah Danner

In court, Mr. Quinn called the case an obvious instance of what is known under New York law as a “justification defense.” Under state law, officers can use deadly force when they reasonably believe deadly force is about to be used against them or someone else. Sergeant Barry can argue that he acted in self-defense, former prosecutors and defense lawyers said.

“If someone is coming at you with a bat, that is deadly physical force,” said Marvyn Kornberg, a Queens defense lawyer who has handled police cases.