Late last month, Laverne Dobbinson received a letter, addressed to her son, from a law firm notifying him that it had been retained by the City of New York to collect money for damages to a police car.

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.