This variant targets former victims of scams. The scammer contacts the victim saying that their organization can track and apprehend the scammer and recover the money lost by the victim, for a price. Alternately, the scammer may say that a fund has been set up by the Nigerian government to compensate victims of 419 fraud, and all that is required is proof of loss (which usually includes personal information) and a processing and handling fee to release the amount of the claim. The scammer is counting on the victim’s dire need to recover their lost money, as well as the fact that they have fallen victim before and are therefore susceptible to such scams. Often, these scams are perpetrated by the scammer who originally conned the victim in the first place, as an attempt to ensure the scammer gets every penny possible from the victim.
Source : wikipedia