Mark McManus, who plays Jim Taggart, nearly missed being cast in the series because he was only 5'9". There was a 6-foot height requirement for joining the Glasgow police force, so he would never have made it in at the height.
Series author Glenn Chandler got his inspiration for character names from the gravestones in Glasgow's Maryhill Cemetary.
When this episode was originally conceived, it was as a one-off drama for the ITV network, and in three parts (each 54 mins). At the time, there was no intention for it to be a precursor to a long-running crime series, as STV had no established track record for providing quality drama to the ITV network. 'Killer' was, and remains, a stand-alone police drama originally shot on 16mm and should not be looked upon as a 'Pilot' for the Taggart franchise, despite the similarities in casting that followed.