"Moonlight" hottie Alex O'Loughlin returns to CBS tonight for a guest-starring role on an episode of "Criminal Minds," in which a serial killer sends the team a videotape detailing one of his crimes. On the tape, he includes a plea, asking them to help him stop his killing spree. But first, ET checks in with Alex to get his take on his turn to the dark side.

ET: This role is quite a departure from Mick. How do you think your fans will react to it?

Alex O'Loughlin: How do you think they will react?

ET: I think they may be disappointed. You are not as sexy as you were in "Moonlight."

Alex O'Loughlin: There is more of that coming up. There is plenty of that.

ET: Is that why the part appealed to you, because it was so different?

Alex O'Loughlin: Absolutely. I didn't go to leading man school. I went to drama school. I don't want to play the same role, every role I get. The other thing is, my true fans, emphasis on the word true, will follow me wherever I go. I thought it was a well-earned breather between roles.

ET: Did you do any research on serial killers?

Alex O'Loughlin: Not so much on serial killers, as on OCD. I did a lot of research on Obsessive Compulsive Disorder.

ET: Right, because this character had to open doors twice and not step on cracks.

Alex O'Loughlin: There is more to it than that. OCD is an anxiety disorder. The patterns that people have ... you yourself might have some patterns that you are not aware of. A lot of us do. The patterns that people have in their daily life, such as putting their sunglasses on with both hands, or the way they tie their shoes. There are patterns that we have in real life that ease an anxiety that is inside of us. This is an extreme case of it.

ET: CBS seems to love you. You are doing the new pilot, "Three Rivers," for them. Can you describe your role and talk about the series?

Alex O'Loughlin: We have already done the pilot. The character's name is Andy Yablonski. It is based on a real-life character called Gonzo Gonzales-Stawinski, who is a cardio-thoracic surgeon I have been shadowing for the past couple of months. He has become a great friend of mine.

My character is a cardio-thoracic surgeon. He is a staff surgeon, but he is being preened to become head of surgery at Three Rivers Clinic, set in Pittsburgh. It is called Three Rivers because there are three rivers in Pittsburgh: The Allegheny, the Monongahela and the Ohio, but it is also told from three perspectives: The donor's perspective and the grieving family, the recipient and their family and the surgical team.

It is very different than "Moonlight." It is not about vampires, but there are equal amounts of blood as my last show.

ET: When you worked on "Moonlight," you worked with the American Red Cross for blood donation.

Alex O'Loughlin: That is something I am hoping to take on to my next project. I want to take it to another level and work with Donate Life America, which I will be working with in affiliation with Gonzo and CBS. I want to put something together and do something special for that.

ET: With 'Twilight' now and "True Blood," do you think that "Moonlight" was just one year too early?

Alex O'Loughlin: Many people say that. If they put it on now, maybe less people would have watched it because people are watching the other vampire projects. I just think they pulled it off too early. I think it is a show that took a minute to find its legs, but once we found our legs, our numbers were consistent and we won some awards. We were doing really well and then they canceled it.

ET: Nina Tassler said at the TCA [Television Critics Association] press tour that when they studied the fan reaction to the series, you tested better than the show.

Alex O'Loughlin: That is lovely to hear. It is always funny when you hear things like that, because what do you say besides thank you? I don't get it. I get up in the morning and my hair is all hanging in my face and poking up on one side, I need to shave and I look older than I am. When I stagger into the kitchen to get my breakfast, I don't think, "Oh, look at that handsome guy. Look at that talented special creature."

"The Big Wheel" episode of "Criminal Minds" airs tonight at 9 p.m. on CBS.