Red Light, Green Light - S7-E4
Other mistake: The crash at the start is staged - the semi truck is driving at 20/30mph, is T-boned by the van, and stops instantly. No screech of brakes, no allowance for the driver's reaction time. In the shot of the impact it's moving at barely walking pace, hence being able to stop so quickly.
Chosen answer: M broke into the brownstone and left a note. Holmes deduced he was staying at a high-class hotel from the soap scent on the note, and gave a picture from a hidden camera to his "irregulars" on the street to stake out hotels. One of them saw him, so Holmes followed him to his next intended victim and knocked him unconscious with a baton.
Sierra1 ★