For other people named Jason, please refer to this page.
When "Baseball Hat", one of the bank customers, successfully surprised one of the other robbers known as "Six Foot Five", a gun came within reach of Kate. Kate claimed not to know how to use a gun. Immediately thereafter, Jason dragged Kate into an office and laughed about her claim, then the two of them began to kiss, revealing they were involved in a relationship, and that Kate was an accomplice to the robbery.
When Jason wanted to kill the hostage bank manager Mr. Hutton, Kate decided to prevent it by shooting Jason in the leg. Kate's true motive was to retrieve the toy airplane, and at the end of the flashback, she left with it, leaving behind the money, as well as Jason and the other robbers.