Plot Complication Idea

The recent activities of a serial killer have made it hard for the party to move within a town important to their quest. So for example the killer disguises themselves as an uncommon race that happens to be in your party, and so the town guard have become more apprehensive towards members of that race. Or as another example the killer could bare an uncanny resemblance to one of the party members, leaving the rest in a race against the clock to prove the accused's innocence.