It is pretty much unknown. For the police it was a quite hectic time, chasing the Joker and now they had to chase Two-Face. When asked, Nolan responsed with 'I will answer this question one day, but not today'. Shortly spoken, he doesn't want us to know (yet!). Perhaps it will be a subject for Batman 3?
What also could be an explaination is that either Gordon or Nolan made a mistake. Could be either Nolan who didn't count right, or Nolan who made Gordon make a mistake. After all, they're both human
Here's more information about who the 5 could refering to:
http://www.imdb.com/title/tt0468569/faq#.2.1.134David emerges from the store slowly. He braces himself against a parked car and then keeps on walking in a nightmarish daze.
WE PULL BACK as David blends in with dozens and dozens of ordinary people, walking on an ordinary street, in an ordinary city.
