[spoiler] What exactly tipped off the main couple about
Galbraith?
Just watched this film for the first time, and while I had a hunch about Galbraith right from the start simply because of the way his character was portrayed, I was nonetheless a bit surprised by the seeming abruptness with which the main couple suddenly seemed convinced that Galbraith was the leopard man, immediately setting up an elaborate plot that culminated in a scene that seemed predicated on the knowledge that darkness would be Galbraith's trigger.
Did I miss the mention of a vital bit of information somewhere? Not long before, they had spoken of Galbraith as a nice man whom they both like. Then the man asks the police officer to go talk to Galbraith, and then suddenly the police officer interprets this as the making of an accusation, and then the couple pursue Galbraith on their own, eventually getting a confession without too much difficulty.
What did I miss?