Jimmy's entire plan to get Janni out of the picture. With Frankie as The Mole, he sets up Janni to bring a small force of his men up to Canada to take him out, but Jimmy reverses it and kills all of them. And if Oz hadn't gotten Cynthia to safety, he then could have killed Cynthia and gone back into hiding with the 10 million dollars the assassination plot centers on. Leading into...
Oz comes up with a plan to let Jimmy get the 10 million without having to kill Cynthia. Using his dentist's office, they carve one of the corpses to have identical teeth to Jimmy, then destroy the body with Janni's in a car fire. The damage is so severe, the corpses have to be identified using dental records; Jimmy is declared dead along with Janni, Cynthia retrieves the money and deposits it in Jimmy's account, and not only does Jimmy get his money but he's now legally dead and off the radar forever.
Lazlo Gogolak in the sequel then puts two and two together (Oz is a dentist that was Jimmy's neighbor, eh? Jimmy just happened to die in a mysterious car fire and was identified by dental records, eh?) to figure out Jimmy faked his death with Oz's help.
Oz will be taking Jimmy to an art museum while Cynthia and Jill get the money, as there's cameras and people in a museum and Oz is "being careful." Except the cab driver he hails to pick him and Jimmy up is driven by Frankie, and they're on their way to the marina.