Sarumans Orcs

Greetings!
My fist question as a complete new member:
I have been assuming that Saruman crossed men and orcs to create the Uruk Hai. However when going through the books I only found one implication that this is the case. In thet two towers Fangorn once says that ha might have crossed orcs and men or that he have destroued men. Is there any other implications that Saruman acctually crossed men and orcs? [img]smilies/smile.gif[/img]