It can be for a number of different reasons. The exact details I don't have here, but I have enough to give you a pretty good idea.
We had 19 voluntary withdrawals from the program in a three-year period, from April 2004 to April 2007. Out of that, we had three who returned to the area of threat. So they made the conscious decision to voluntarily withdraw from the program and go back. We had one who thought it was too strict for family visits. One agreement was breached for association with gang members. One witness didn't want to comply with the terms of the protection agreement any longer. We had one who was charged with theft under $5,000. We had cases where people were using drugs, and they didn't want to stop, so they withdrew from the program.