Mastic PD exists within the producer John Sheehan's "Ormsbyverse". It is a prequel series to Sheehan's forthcoming "Death Mask: An Ormsby Mystery".
Mastic PD was originally supposed to be a prequel film, but series writers Patrick Devaney and Lauren Clover realized that they had much more material and turned it into a series.
The character of Ian was originally supposed to be a one off character and be off the show after the series premiere. But, Patrick Devaney and Lauren Clover enjoyed writing for the character and decided to bring him on as a series regular.