Joe Mantegna and Daniel J. Travanti, <I>Criminal Minds</i> Joe Mantegna and Daniel J. Travanti, Criminal Minds

Criminal Minds' Behavioral Analysis Unit has an obligation to keep bad guys off the street. But series star Joe Mantegna says every case isn't just about right and wrong.

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"Sometimes when a case gets resolved, there's always different aspects to consider. It's not always so cut-and-dried," he tells TVGuide.com "There are sometimes conditions that lend themselves to why these things happen. It's interesting when the stories have a little bit of a twist to them."And Wednesday's episode (9/8c on CBS) has just that. When the BAU begins investigating a string of murders, Rossi (Mantegna) can't help but notice a similarity to a killer he chased over 25 years ago. Just when Rossi got close, the killer stopped, never to be heard from again — until now.Emmy winner Daniel J. Travanti

(Hill Street Blues) guest-stars as the killer, who, in his advanced age, has developed Alzheimer's disease and is repeating his murders because he can't remember them.

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"It's such a prevalent condition right now," Mantegna says. "It's on a lot of people's minds and has gotten a lot of attention over the last 20 or 30 years. It's a realistic thing, and I thought it was an interesting spin on it. It's something that's rampant in the elder community, and it would certainly be just as rampant among the serial killers."But because of the killer's condition, Mantegna says it may be difficult for Rossi to take any satisfaction in finally cracking the cold case. "We tweaked the end just a little bit to make another point that I thought was important," Mantegna says. "On one hand, [the killer is] somebody who's obviously a bane on humanity who spent a good portion of his life as a murderer. Yet on the other, he is now very sick. How much joy does one derive in that? There's relief [for Rossi], but the joy is somewhat tempered because this guy is in a prison already."But Mantegna's not sure if viewers will have sympathy for Travanti's twisted killer. "I think there will be some sympathy for the condition," he says. "I think people will be able to relate and say, 'Oh, God, that's the same thing Grandpa's got. But then I think the next feeling might be, 'Thank God that's not what Granpda did!'"