The internal-affairs honcho who headed the NYPD�s explosive ticket-fix investigation filed for retirement yesterday, The Post has learned.

Internal Affairs Bureau Deputy Inspector John McDermott, 46 � in charge of a probe that led to the indictment last month of 16 cops for crimes including official misconduct and conspiracy � earned $146,364 in 2010, records show.

�People don�t understand why now,� one puzzled source told The Post. �It doesn�t make sense.�

The shocking ticket-fix case is far from over, insiders note, and McDermott�s participation will be crucial.

As The Post reported last May, McDermott himself allegedly arranged for a speeding ticket to disappear. The NYPD denied the accusation.

A woman answering the phone at McDermott�s home last night declined to comment.

(Source: NY Post)