As I just mentioned in this other thread, after reading the court documents I believe the other crime is tax avoidance and that they have a case regardless of whether or not campaign finance violations are involved.
I also personally know of cases where people were prosecuted in NYC for tax and financial crimes involving much smaller sums of money. I know an NYC businessman that was criminally prosecuted for tax avoidance for buying gifts out of state to avoid paying NYC sales tax, the amount of tax he evaded was less than $200.