Hey all, I've been an avid fan of CSI since it came out and a frequent visitor to Talk CSI for a while but I thought I'd throw in my few cents.
Hodges is too obvious. It's a CSI writer's thing to throw us red herrings. Remember last season when a lot of us thought that Brass was going to die? And when we thought we'd see a Grissom/Sara scene where maybe he asks her out or something and then we find out they've been in a relationship for a while? CSI writers are known for going completely off the beaten path and that's what made the show survive so long. Even 24 is nowhere near the ranking of what CSI is.
My thought is that it's CSI Henry Andrews - Toxicology expert. The actor, Jon Wellner, is a "researcher" for the show. If they kill off his character, he's still with the show. Basically Wellner is a fill-in actor for a character that has rarely showed up until recently...(
http://www.crimelab.nl/characters.php?series=1&lname=Andrews&fname=Henry)
Henry was added last season and it would be much less of an impact for the show to get rid of one CSI that's only been there for two seasons and has hardly any screen time than a character that they've developed like Hodges. With Henry Andrews, we hardly know anything about him meaning the writers can now develop a bigger plot with him in it.
Henry also has a lot of knowledge in toxins. The second and fourth victims were poisoned (second victim convulsed and bled out from the pane of glass, the fourth victim was CO poisoning created by a combustion reaction). The first victim (Izzy) was a fairly large man and probably very capable of defending against an attack to the head. It would take a lot of stealth and strength to hit him in the head so right that a single blow would kill him. Wouldn't it be easier to make him drowsy and weak first, then hit him in the head? The third victim was found in the pool of water and electrocuted. How would the killer place the third victim there? It would be so easy if he was drugged. Henry, being a toxicology expert, would have the knowledge on what toxins to use that would not leave a trace on the body (plus it wouldn't be toxins that killed the victims, it would be some other form - but toxins will be used to weaken them). Henry would also be the person able to hide results from the other victims of any toxins in their system.
My theory is that Henry Andrews is the MCSK. He probably has connections to Sara somehow, possibly a stalker, got a job at CSI last season because of Sara, found out that Sara and Grissom were together, went nuts, killed a bunch of people to try to get to Grissom, and finally when Grissom figures it out, he's taken hostage?
Grissom as a hostage instead of Sara would be more interesting in my opinion. Sara would have to pick up the MCSK investigation with Catherine (who will take over for Grissom) and find Grissom. We'll see a lot of Sara drama and Grissom drama in the same episode. In the end, Sara could end up shooting Henry to save Grissom and since she has said she couldn't take another person's life, it could (along with the plot in Empty Eyes) could have a huge psychological effect on her forcing her to resign (if Jorja Fox doesn't re-sign). That'll leave it open as well for Jorja Fox to return in the future as a guest or as full-time (after Sara has "recovered").
It wouldn't be the first prime time action/crime drama to have a new character that was a stalker/killer. In NCIS, a new lab tech applied for the job to frame an NCIS agent. In Cold Case, the finale involved a serial murderer who was a file clerk. So if the writers go with the Henry as MCSK route, then it'll be interesting to see how they spin it since two other CBS shows in the same category as CSI have done the same thing too.
p.s. how do I apply to be a writer for CSI? j/k