Theories on why he stopped?

While Zodiac did stop on his own, I think the reason he stopped was because it added a mystery. There is a documentary out there that's 7 minutes long called Zodiac: Sign of Death. It came out in 1978/1979 so 10 years after the killings started and didn't give out too much details. They left out names of surviving victims but for some reason put in the riverside killing.

Anyways, the ending of the video asked "where is Zodiac? Dead? In prison for some lesser offense? Or is he safely in a mental institution? Did he lose his lust to kill and returned to a life of non violence? Or, is he waiting" I think someone like Zodiac enjoyed the idea of sitting there and adding paranoia.