Thrillers are all about keeping the audience on edge with tightly built suspense, rewarding their patience with cathartic excitement. Nowhere in that sentence does it say that a thriller must necessarily move fast. Indeed, throughout the genre's history, some of its best outings have been undeniably slow-burning, demanding even more patience from the audience than usual and rewarding it with even more satisfying releases of such tension.
These movies have come from all over the world, all throughout history, spanning several different kinds of subgenres, tones, and styles. Whether it's a noir, a detective tale, an action flick, or a dramatic character study, these thrillers prove that "slow-paced" is very much not antonymous with the concept of "exciting." At their best, they can be some of the greatest films of all time, rewarding their viewers' loyal patience.