A bit from William Fichtner on AICN:
Capone: Are you presently shooting TEENAGE MUTANT NINJA TURTLES right now? Is that where you are?
WF: Hey listen, if I tell you I’ve got to go after you. [laughs] Yes, I am. I’m in the middle of it right now, yeah.
Capone: Tell me about playing The Shredder.
WF: Listen, are you ready for the politically correct answer? I play a guy named Eric Sachs, who goes through changes.
Capone: Got it.
WF: Okay, there we go. We’ve got that out of the way. No, you know what? Kind of similar to THE LONE RANGER, this came up very quick, and I was literally flying back from Santa Fe having worked on Tommy Lee Jones’ film, THE HOMESMAN, and I’m in the airport in Santa Fe, and by the time I got home, I had to read this, because I was going to travel like two days later. And I read it and I talked to my representation and my wife, which is the head of the representation, and I said, "I’ve got a feeling this is cool." And I’ve worked with Michael Bay before, and that gives it an awful lot of pop right there, but it was more than that.
I spoke to the director and some of the producers on the phone and I knew that what they were going to make…. See TURTLES was not my time; it was my niece and my nephew's thing. They're in their 20s now or early 30s. I called them up and said, “Hey, what do you think about Uncle Bill doing this?” They were like, “What do you mean what do we think about it? You better do it!” And I’m really glad that I did. I think that whatever I remember of the Turtles being more cartoony, and I don’t mean that as a knock, it’s just what I remember, that’s not this. This is cool. This is a little wild. It’s a little freaky. I’ve been having an excellent time working on it.
Capone: Ninjas should be cool, of course. Why wouldn’t they?
WF: Yeah, it’s been a real character to explore, and we're figuring it out. This guy has grown a lot more since the day I got off the plane to start working on it, that’s for sure.