Legal Question in Civil Litigation in District of Columbia

The interest rate that you would claim would likely be the APR specified in the lease itself (if any) or if none is referenced, then the answer would likely lie in the DC landlord-tenat law that was applicable at the time to such matters. However, given the amount of time that has elapsed, any such claims that you might put forward at this late date would likely be subject to DC's statute of limitations law and hence uncollectible(in my opinion).