I found this interesting little history page about SF Chinatown's Tong Wars in the 20s, that ends on a violent footnote:
Drug use in the 1920's was not restricted to opium dens of the Chinese Tongs. Heroin, a new drug formulated to help addicts of opium break their habit, had begun to appear in San Francisco. Retired Officer Charles Foster recalled his first experience with heroin users.
"There was this guy named Kelly," said Officer Foster, "who went on a rampage one night in the 1920's. He got himself all hopped-up and got a gun and jumped into a cab, and he told the driver to take him to Potrero Hill. There was this old guy there just getting dressed up to go to a restaurant for dinner. He was walking down the sidewalk toward the Mission, just minding his own business, and Kelly jumped out of the cab and shot him, for no reason. Then he went on a rampage. He took over the cab and took off over the Hill, and he shot two more people in the chest down around 11th and Folsom. He drove all over town, and he took a shot at Chief O'Brien down around Fisherman's Wharf, although I don't think he knew who he was. The Chief just happened to be there on his way to dinner. Finally, they tracked him down in some cheap rooming house South of Market, and they got him after a shoot-out. That was the first I ever heard of hop, but we sure heard a lot more about it after that. That was the start of the whole thing."
Congratulations, Kelly! Boldly breaking new ground. Now there's some Irish pluck. (Link found via peterme