1)Jack was justified b/c the giant killed his father and stole Jack's wealth, therefore Jack was just taking back was rightfully his.
2) Jack was saving mankind from a cannibalistic murderer who enjoyed grinding the bones of boys and eating them.
and point 3) Jack may have been smart academically, but he was still young and his brain hadn't matured enough to know right from wrong. After all....teenagers do stupid things. LOL!
She had to come up with some evidence, so Kate and Carter become Exhibit C.
I'm not sure who cracks me up most here, the contriver of the evidence, or the actors who portrayed it so well.