The roles in this game were in fact chosen at random. I did not tweak the roles.
I had my nine year old daughter (Tori) write the names of the players on pieces of paper and place them in a hat. This gave her something fun to do since she had been driving me crazy at the time.
I decided that the first three names she drew would be Det, Dr, and Vig. The next four names would be the Don, snitch and two goons respectively.
When this was done, she asked, "What about the rest of the names?". "The rest are all townies", I responded. "OK", she said, "lets draw for Townies". I let her continue to draw the names of the townies, as I pretended to write them down. I didn't have the heart to tell her we didn't need to draw for townies.