Sampling for rare events

I am trying to estimate the event rate in a population where the event by definition (Money laundering ) is rare by drawing a representative sample. Assuming an event rate of 1 %, I calculated the sample size to estimate the event rate in the population using the general sample size calculation formula(Z^2 *p*(1-p))/c^2
z -> 1.96 (corresponding to 95 % confidence)
p-> event rate(1 %)
c(margin of error)-> .005 (50 % of 1 %)

Is this a sound approach.?Are there any other rare event sampling techniques I can use?
Any inputs would be greatly appreciated!