The Zodiac killer was one guy, I believe. I've looked at all official reports, multiple times. He was 5'8' to 6'0", stocky build, and was 30 or younger: this was directly from the two victims who saw and/or heard him from just a couple of feet away. The reports of 40's in a single incident happened from witnesses who were not close up. However, out of all of the sightings in confirmed offenses, one thing never changed: stocky build. That's interesting because in 1969, overweight and obesity rates were significantly lower for younger people indicating this man was a little more distinct from his contemporaries. There's no way to prove it was more than one guy and it is not logical based on what we know about the crimes and the confirmed Zodiac communication.