Derek Morgan:  Does anybody here know exactly what a serial killer is ?
David Zimmerman: Someone who 's committed more than one murder .
Derek Morgan: That 's very good . By statute , _ three _ is the magic number . And it 's actually more qualitative than quantitative for us .
David Rossi: Today we 're going to talk about how some serial killers get made . Because if you can understand that , then you can figure out a way to catch them .