Raymond Russell, a realtor with an office across the street, said he parked his motorcycle in front of the vehicle that week and would have looked right past the dead man toward oncoming cars before crossing. He found it impossible to believe the body was there as long as it was.

“I don’t give him a week here,” he said. “A couple days, maybe.”

Traffic officers who write parking tickets most likely passed by him at least twice, on days that his car was parked illegally. Officers looking for violators on street-cleaning days — on East 12th Street, those days were Tuesday and Friday — routinely ignore vehicles when the driver is sitting inside. Mr. Weglarz’s vehicle received no tickets on the Tuesday or Friday when it was parked illegally, suggesting an officer might have seen him and assumed he was just another idle driver.

A couple people visiting the garden on the corner and its neighboring playground complained to a garden manager about what smelled like a dead rat. The manager actually found a dead rat and disposed of it, but the smell lingered on and off.

In the middle of the week, Anthony Greenheck, walking his dog late one night, noticed a silhouette of a man behind the wheel. He thought it was an Uber driver napping between calls. But when he saw the man had not moved two days later, he approached. The windows were tinted.

“I peeked a little closer and I decided to knock,” Mr. Greenheck said. “No movement.” He called 911.

When firefighters and the police arrived and opened the vehicle’s door, a powerful odor filled the block for hours. Officers raised a curtain around the vehicle, obscuring the body inside as it was removed. A freelance photographer who lives across the street, Bob Krasner, went to his window and took pictures of the scene. “I must have walked by that car at least a half a dozen times while he was there,” he said later in disbelief. “I’m fairly observant.”

A final resting place

The episode left Mr. Weglarz’s family furious with the police. They don’t believe the chances were high that their brother could have been rescued after ingesting the poison, but they said he should not have been left there for a week.