The attack on Mr. Rivers unfolded in seconds on July 21.

It happened during the most quotidian New York ritual: alternate-side parking. Ms. Belis and Mr. Rivers were sitting in their car just before 1 p.m. eating pizza in front of their walk-up apartment on Decatur Avenue, waiting for street cleaning to wrap up, when Ms. Belis heard her husband suddenly ask someone, “What do you want?”

When she looked up, she saw a man in a black ski mask standing outside the driver’s side window, she said days after the attack. Within seconds, Mr. Rivers had been stabbed in the chest and had jumped out of the car, struggling with the attacker over the knife. Ms. Belis jumped into action with a crowbar.

Minutes later a downpour began, and the attacker escaped as Mr. Rivers collapsed.

It was raining so hard and so fast that Ms. Belis couldn’t find a wound where pressure might stop the bleeding, she said.

“My husband died in my arms,” she said.

Franklin Mesa, 19, was arrested in connection with the attack, the police said. He was charged with murder, manslaughter and criminal possession of a weapon.

Mr. Mesa’s grandmother, who declined to speak with The Times, told The New York Post that he had been on medication to treat schizophrenia for multiple years. Later, his lawyer asked for a psychiatric examination to determine whether he might be incapacitated and unable to stand trial.

The community has few easily accessible resources for mental health care, especially for families who want to get their adult relatives help, said Daniela Tuda, who spent a year working as a social worker at Bronx Community College. People fall through the cracks because of overburdened social workers, lack of trust in clinicians, workers who don’t know how best to treat patients or because of a simple lack of appointment slots, she said.