Why did Procopius hate Justinian?

In World History a few days ago we were asked to find out why Procopius (the author) hates Justinian. When he was alive Procopius wrote about his greatness but after his death he wrote the "secret history". We were asked to find out why he hated Justinian enough to write this and I can't find it anywhere on google. Any ideas? Nothing long, its just a discussion we are going to have in cl.