Put it at the end of a setup scene, just before the cut to the new location or the hidden clue, then follow the reveal with Hello Darkness My Old Friend or an Evil Laugh when the culprit is finally shown.
About this sound
A nearly 14-second dark piano sting, made from low notes played slowly and left to fade one by one, with no tune to follow. Its heavy minor sound feels cold and unsettled, turning an ordinary moment secretive and threatening. It leaves a listener expecting a reveal, a betrayal or bad news before anything has happened on screen.