If I remember correctly, Near had one of his agents trail Mikami then snuck into his locker or case of some sort, then switch the death note that Mikami had for a fake one, created by Near's men....
Okay, people. The movie is call "Death Note: The Last Name". The Death Note is an other wordly book that holds the power to kill anyone that has their name written in it, as well as the way they die...