I guess for me that is not clear-cut. Rapes still occur pretty often, and many/most sadly aren't reported. (Legalizing prostitution could reduce them?)
For every traffic violation that is caught, a high multiple more fly by. (Speeding, for example).
The demand for murder is so low that it's hard for me to conceptualize as a market.
Of course you can. Works perfectly well for rape and murder, for example. (As well as for traffic violations, for that matter.)