A New York City agency charged with investigating police wrongdoing on Thursday forced an employee to resign after discovering that the employee had leaked the disciplinary history of the officer who placed Eric Garner in a fatal chokehold. The agency also confirmed for the first time that the records, which showed that the officer faced no stronger punishment for abusing his authority than retraining and the loss of two vacation days, were authentic.

The resignation, coming a day after the New York Police Department publicly railed against what it called an illegal and improper leak, again brought into focus the city’s strained position on police transparency. Mayor Bill de Blasio has called for overturning a state law to allow the city to disclose details about disciplinary actions taken against police officers, even as the city has been fighting in court to prevent the release of those details about the officer, Daniel Pantaleo, who put Mr. Garner in a chokehold in 2014.

The employee, who was not identified, was a junior staff member who had worked at the agency, the Civilian Complaint Review Board, for less than a year. The person had not been involved in investigating any of the misconduct cases in the disciplinary records of Officer Pantaleo, which were published this week by the liberal news site ThinkProgress. The employee resigned on Thursday after being faced with the prospect of being fired.

“After a swift and thorough internal investigation, the Civilian Complaint Review Board identified the employee who was the source of the leak,” Jerika Richardson, senior adviser and secretary to the board, said in a statement. “As of today, that individual no longer works at C.C.R.B.”