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)