Mr. Murphy’s killer was not prosecuted, Detective David Gregory said, because he appeared to have fired in self-defense. Barry Washington’s death was collateral damage — a stray bullet, meant for Dawaun.

Nine months later, Mr. Washington’s family is still reeling. His mother, a cancer survivor, is virtually a shut-in. “We loved him dearly, and with a pull of the trigger, he was gone,” she said. “That I cannot accept.”

Jaci Washington’s 10-year-old son is withdrawn and angry. Her 14-year-old daughter has nightmares. Her brother, she said, probably would have counseled her to forgive his killer. “He kept telling me, ‘You have to look for the good in everybody, ’” she said.

But she says she cannot forgive. She grasps for metaphors to capture the family’s loss. “It’s like the world crashing in. It’s like a nuclear bomb went off on my couch,” she said. “It’s like someone hit ‘pause’ in my life. I just saw him, and I will never see him again.”

Mr. Murphy’s mother is not seeking forgiveness. In an interview, she said she did not believe her son had fired a gun at anyone, insisting that the police had botched the investigation and let the real culprits go free. And she is angry with Jaci Washington for characterizing her son as a murderer at community meetings on gun violence.

Ms. Washington and her mother no longer go to those meetings. They seemed futile, they said — more broken people, describing more senseless deaths.

“I don’t want pity. I want results,” Jaci Washington said. “One more black shooting in a black neighborhood. ‘Let’s rally around.’ It’s a facade. When all is said and done, we’re still left with the grief.”