If the letter, which demanded that he pay $710 within 10 days, was pro forma, the circumstances surrounding how the damage occurred were most certainly not.

The police car was damaged after a chase that ended when it collided with Ms. Dobbinson's son, Tamon Robinson, denting the front of the car and killing him.

On Friday, the law firm handling the collection effort said it had formally dropped the effort. Paul J. Browne, a spokesman for the Police Department, said his agency did not send out the letter and referred the matter to the city's Law Department.

"We don't know any instance where we send letters like that," he said. "I'm not sure how it came out."

Kate Ahlers, a spokeswoman for the Law Department, said the notice had been sent in error after her department received  a referral from a unit of the Police Department. "We regret that Mr. Robinson's family received a collection notice," she said in a statement, adding, "We recognize that this involves a tragic case."

At a news conference on Friday and in an interview afterward, Ms. Dobbinson, 45, a driver for the Access-a-Ride service for people with disabilities, said she felt "disrespected" by the letter.

"I was humiliated that they're sending my son a letter for the car that killed him," she said, her voice faltering with emotion. "They killed him; let him rest in peace."

Her lawyer, Sanford Rubenstein, called the collection effort a "disgrace" and "heartless."

"How dare the City of New York direct their lawyers to demand money and threaten collection procedures for property damage to a police car which struck and killed Tamon Robinson under circumstances in which the actions of the police officer operating the police car that night are the subject of a criminal investigation," Mr. Rubenstein said in a statement.

"They have to realize this letter will be received by his mother, who is still grieving his wrongful death," he added.

The existence of the letter was reported on Friday by The Daily News.

Cristina Gonzalez, a lawyer for the collection firm, Linebarger Goggan Blair & Sampson, said that it had received the Robinson case as one of a number of collection cases referred by the city and the Police Department, but that once it became aware that Mr. Robinson had died, it "ceased collection."

"We were not aware of the circumstances," Ms. Gonzalez said. "This type of receivable is not something we pursue when the alleged debtor is deceased."

Mr. Robinson, 27, a muffin shop cashier, was killed in the early morning hours of April 12 when he tried to flee police officers who had spotted him digging up decorative paving stones from the grounds of the Bayview Houses in Canarsie, Brooklyn, where his mother lived.

Mr. Robinson illegally dug up cobblestones and sold them to scrap dealers, a sideline that had gotten him arrested numerous times.

The officers followed him for about 100 yards in their car, turned up a fenced-in sloping walkway to the front door of his mother's apartment building, then veered into his path. The result was a collision that left a large dent on the driver's side of the car just above one of the front tires.

Police officials have labeled the death an accident, and the initial police report said Mr. Robinson "did run into the side" of the police car and fell backward onto the pavement, causing the fatal injuries to his head.

An autopsy report released in June by the city medical examiner's office found that Mr. Robinson had sustained "blunt-impact injuries of the head, torso and extremities," including "traumatic brain injury" and several hemorrhages. It described the manner of death as an "accident (struck by police vehicle during pursuit)."

Mr. Rubenstein, raising the issue of what he called a police cover-up, said the "head injuries were inconsistent with Tamon running into a car."

Mr. Rubenstein has filed notice that he will file a lawsuit on behalf of the family seeking $20 million for what he termed a wrongful death. The episode is also under investigation by the Brooklyn district attorney's office.

This article has been revised to reflect the following correction:

Correction: October 5, 2012

An earlier version of this article misidentified to whom the collection letter was sent. It was addressed to Tamon Robinson, not his mother, Laverne Dobbinson. The error was repeated in the headline.