I just pick up on totally trivial things that are mentioned in the show as there is only one reason for them being mentioned.
Going with this theory actually threw me off on the recent exorcism episode of Psych.
The big guest star was Ray Wise playing a priest, but he was also the first suspect. So clearly he didn’t do it. I was convinced it was the other priest simply because he had enough speaking lines not to be filler, but he really didn’t have a function in the episode, either. Also, the actor looked familiar. But he wasn’t the bad guy.
I’ve definitely had the experience the OP describes, where just the choice of actor gives it away. We’re finally watching season 1 of 24, and I just knew the instant “Janet’s dad” was shown, there was no way they hired the freakin’ Sentinel just to be someone’s worried dad.
Also, Ebert refers to the Law of Conservation of Characters - not a big thing in books, which have more leisure to jerk you around, but in TV and movies, if they pay someone to have lines, you know they’re not inconsequential. Realizing this definitely transformed my experience of entertainment.
I haven’t watched recent episodes, but *Monk *used to do this. We (the viewer) often knew who the killer was, but half the fun was watching Monk figure it out.
If there is a ‘good but boring’ husband, and he doesn’t get killed early in the episode, like a red shirt security guard on Star Trek, then it is always he who is the murderer. Invariably, if the husband is alive and in scene 3, he did or will do it.
If he gets killed early, then it’s fine, because a more dynamic hero will then be injured and ‘almost’ killed saving the former wife. Love happens, cue credits.
Good and boring gets a husband killed every time. Unless he’s evil.
Call casting. “Get me that weak husband type who’s always getting killed.” Oh, and send that guy who always kills him.
I think I’m the person these shows are made for. I have the very real ability to suspend reality and let the writers/actors take me where they want to take me and how they want me to get there. I just get to sit back and enjoy the ride. It has happened that I’ve caught on to the killers early and those times are very unsatisfying to me. Luckily, it doesn’t happen that often.
I can even pretty much do this with things I haven’t seen in a while as well. I’ll know what’s going to happen but for the couple of hours I’m involved, I can easily forget what I know and take the ride over again.
They did do that once, actually, in an episode of Angel.
They didn’t put Juliet Landau’s name in the opening credits of the episode where Dru shows up to re-vamp Darla. It was startling.
I don’t know why they didn’t do it more, though.
*Six Feet Under *did the same thing once.
There was an episode when Brenda’s brother Billy showed up suddenly. He wasn’t listed in the opening credits as a guest star and it was a shock to see him appear.
*Buffy *also did it when Giles returned to kick Willow’s ass.
That is one of the best and creepiest eps of L&O: CI ever!!
Or get the stereotypical bad-guy actor like Joey Pants on . . . then have it be someone else.
I thought the whole point of the “police procedural” genre was that the point of the story was not the whodunnit aspect but the how-they-figgered-it-out aspect.
Not a detective series but was an excellent war series Band of Brothers used mostly unknown actors so that you couldn’t predict who was going to live and who was going to get killed off.
David Schwimmer played a total arsehole who didn’t figure much after the episode about training.
(For which he has my total respect as a famous actor taking an inglorious role)
Tom Hanks had a very minor, one off part in an episode,so much so that I personally didn’t even peg him.
A pity that more T.V. series do not follow this example to make programmes more interesting for us.
I’m a bit flabbergasted by how many people in this thread actually read the cast credits at the beginning of a show. Who *does *that ?
In an episode of Babylon 5 a character makes an appearance after having been missing for a season or two. Her name is listed in the opening credits as a special guest, so, for those who pay attention to the credits anyway, her appearance was not a surprise. The creator of the show, JMS, stated that there were certain rules that have to be followed when it comes to giving actors credit. It isn’t that producers are stupid when they do this they’re just following the rules.
Oh yeah. I’ve watched pretty much every episode of all of the L&O franchises, and I just started watching NCIS on USA last week - and I’m pleased that my “sixth sense” (ha) for crime shows works on non-L&O shows. 
Some of it is, “oh, that guy!” and some of it is, “they wouldn’t have made such a big deal about that character if she wasn’t significant” or, “huh, that camera lingered on that character just a little too long - she’s got something to do with it,” and some of it is just knowing the genre and how they like to try to surprise you at the end.
But there’s one character actress who’s always the “bad guy” if she’s on - I can’t find the names of the episodes she’s been on, so I can’t find her. But if she’s on, she’ll definitely have done it.
I think the rather obvious answer is, “Anyone who wants to know who’s going to be on the show they’re watching.”
Hell, with some shows (like The Sopranos) you even have to pay attention to the names that run during the main credits, because they change to reflect which actors are actually in that episode.
That’s what was great about Columbo - you saw the whole crime and the criminal right at the start, and the rest of the show was Columbo investigating it, questioning the killer while he/she squirmed and offered suggestions as to what happened, as he was really putting it all together while working under the guise of being a bumbler.
That’s my Hollywood whodunit theory: “whoever has the next most lines is the killer.” The obvious bad guy? No, he didn’t do it. It’s the person who has a speaking role that doesn’t otherwise merit any screen time.
For example:Presumed Innocent. I knew it was his wife because her alibi wasn’t great and she was the only other character in the film who had a decent sized speaking role.
There’s an episode of Numb3rs with Bruce Davison in it. Unless he’s a regular, when is Bruce Davison ever anything but the bad guy? I totally nailed it.
Well, it was a double-switch, which I bet was deliberate. He wasn’t the bad guy after all.