Outlawing alcohol did not stop drinking; it drove it underground, where people drank whatever was sold, including toxic wood alcohol. The ban meant to protect people ended up poisoning them, which is why a city medical examiner blamed its backers.
A poisoning can look like natural death, so a new science was needed to tell the two apart. By testing tissues for specific poisons, forensic toxicology made cause of death something that could be established rather than guessed. It was built one poison at a time, each needing its own experiments.
When chemists can make new deadly compounds but no one can yet detect them in a body, poison becomes the killer's weapon of choice. The gap between making a poison and being able to prove it was used is where murderers get away with it.