How is Zaroff able to finance his lifestyle?

Zaroff financed his lifestyle off of the money he made from good investments.

"After the debacle in Russia I left the country, for it was imprudent for an officer of the Czar to stay there. Many noble Russians lost everything. I, luckily, had invested heavily in American securities, so I shall never have to open a tearoom in Monte Carlo or drive a taxi in Paris."