This has to be the biggest error (or "boo-boo" as Z would put it) in the police handling of the case. It throws Fouke and Zelms from possibly catching Zodiac (or perhaps ruling out an innocent white male suspect in the immediate vicinity while Z is still at large, thus beginning a manhunt), it puts a false construction on the crime scene as one of opportunity rather than premeditated homicide, and it made SFPD more guarded in how they discussed the case.

All these things contribute to the killer escaping in a way that boils down to police mismanagement. I don't see police missing many other opportunities. Cecilia Shephard could have been saved with quicker action, but that's not on the police as I see it.