Okay, the mainstream opinion here says that it was Fredo who opened the drapes. But when should he have done it?
1) Before Kay went to bed? Then why didn't Kay close them?
2) After Kay had gone to bed? Was it normal that Fredo walked around in Michael's bedroom? Where Michael's wife sleeps (did Fredo sleep with her?), where his children play with their toys (was Fredo looking for a toy)?

Who could open the drapes without getting the attention of Kay? Kay herself? Was Anthony paid by Ola? Did Michael open the drapes, but then forgot to close them?

Or do we just have to acknowledge that the whole drape-openening thing is bad writing?