CSI: Crime Scene Investigation/WMG

Horatio Caine is suffering from severe Post Traumatic Stress Disorder.
Horatio's complete lack of a sense of humor, his extreme determination and ruthlessness with bringing criminals to justice, and his overprotective nature towards the innocent (especially children and families) seems to indicate that the events of his past as a soldier and the loss of his brother affected him a lot deeper than anyone knows. He either cannot or will not come to grips with it and move on.
 * That would explain the one liners...

The CSI universe is the past of the Judge Dredd universe.
The multi-dutied CSIs will eventually gain more and more responsibility legally, until they are the polydutied, fascist Judges. Grissom will obtain immortality and become Judge Dredd.

Horatio Caine has Asperger's Syndrome.
This explains his inability to make eye contact and his troubled relationships. He also has odd postures, "stimming" with his sunglasses, and a hyper-focusing trait wherein he is obsessed with certain trivia (bomb squad, anyone?)...

Horatio Caine is an Alternate Universe version of Rorschach
He has red hair, odd facial features, and a messed-up family. He considers his coworkers to be his Nakama - possibly his only nakama. He has incredible detection skills and is master of the Click Hello and snappy one-liners, and is terse in general. He appears to have ninja skills.

The split happened because he went to seminary (Walter's casefile mentioned he was doing well in religious studies) instead of the ladies' clothing factory.

All three shows are set Twenty Minutes Into the Future.
More like five to ten, really - but this explains both why the Applied Phlebotinum is so much faster and more reliable than its real-world equivalent and why procedures have changed to allow CSI techs to conduct full investigations, interrogate suspects, and so forth. The Vegas show is set a few minutes ahead of the New York show. Miami is set a bit ahead of them both, even though Miami and New York have crossed over a few times. There was an episode of CSI: Miami with a weapon that could shoot a few hundred bullets at the same time. This could also explain why the Miami team's use of a Hummer H2 instead of, say, a Ford Focus wagon or a cargo van, doesn't lead to a taxpayer revolt. By that time, a used H2 will be the cheapest vehicle of any type available- it's well on the way now. The gas for it, on the other hand...
 * Gas? What gas? The team Hummer has undergone conversion to run on alcohol—takes about ten minutes with a needle-nose pliers and a stiff wire.
 * CSI:Miami's actors have claimed that the Miami spinoff is a "comic book world".
 * That would make all of the shows comic books, since they've all crossed over.
 * Maybe this is also why the Crime Lab people have so much more power (in terms of jurisdiction) than their contemporary counterparts do.
 * Bizarrely, this makes a lot of sense.
 * Remember also that in the CSI-verse, the Cumbre Vieja volcano did explode, causing a megatsunami that flooded Miami. The Canary Islands probably don't exist anymore.
 * The hundred-bullet gun is a real concept with working prototypes. The fact that only prototypes exist now in Real Life, however...

All three shows are set in the Stargate Verse.
Consider CSI: NY's hologram room and the examples above. It's all a result of the SGC slowly leaking advanced technology into the public sphere.
 * Perhaps it takes place in the SG:A alternate universe in which one Detective Sheppard investigated a series of murders committed by a Wraith in Las Vegas.
 * That would explain how they can afford to build spaceships and set up bases on alien worlds. That would show up in the budget unless someone set up companies to sell alien-derived tech.
 * The vampire fans' scars looked like suckers.

Sara Sidle didn't leave on her own accord; Ecklie forced her out.
Think about it: Ecklie was the biggest opponent to her and Grissom's relationship, and he even threatened to can both of them if they didn't stop. While there's no doubt the Miniature Killer incident shook her up something fierce, it's doubtful that she'd completely abandon her relationship to Grissom - the one thing that made her feel safe and secure - because of it; in fact, part of the reason she changed shifts was to help her recover. The complete 180 of her going from "we can handle this together" to "This Is Something He's Got to Do Himself" is too coincidental to be spontaneous on her part. Hence, Ecklie must've pressured her into retiring to put an end to the relationship and strike a blow against Grissom.
 * Now she's back.
 * Still, the obvious tension between them in the opening of S10E03 adds weight to this, even if Ecklie was the one to bring her back in. After all, he's been gunning for her ever since Season Five, when the only thing stopping him getting rid of her was Grissom's refusal to fire her. At this point, he wants to humiliate her.

Gil Grissom is a superhero. His superpower is competence.
In other words, he literally can do anything he puts his mind to, often without any formal training, at a moment's notice. He even made a makeshift crime scene kit once using mechanical pencil lead and tinting film. He even has an Alliterative Name.

Sara Sidle is also a superhero. She, however, refuses to accept her powers, which is why she is alternately fascinated by and despising Grissom. Eventually, this leads to her breakdown and departure.

Grissom also eventually leaves to attempt to help her come to grips with her powers. Since his superpower is competence, he succeeds.

All CSI teams have a Man Behind the Man who's running the show. All shows.
And (you'll probably see this coming) it's none other than L.
 * Adding to the above theory, the CSIs are orphan's of Wammy's House.
 * Gil Grissom = G.
 * Catherine Willows = C.
 * Nick Stokes = N.
 * Greg Sanders = S.
 * Riley Adams = R
 * Sara Sidle = S2.
 * Warrick Brown = W.
 * Jim Brass = J.
 * Al Robbins = A.
 * David Hodges = D.
 * Horatio Caine = H.
 * Calleigh Desquene = CD.
 * Eric Delko = E.
 * Ryan Wolfe = W.
 * Frank Tripp = F.
 * Natalia Boa Vista = V.
 * Mac Taylor = T.
 * Stella Bonasera = B.
 * Danny Messer = M.
 * Dr. Sheldon Hawkes = Dr.
 * Donald Flack Jr. = DF.
 * Lindsay Monroe = LM.
 * Jennifer Angell = JE.

Horatio Caine is an Agent.
Think about it. Sunglasses and dark suit - check. Deadpan line delivery - check. Ability to conjure items from Hammerspace - check. All he needs is a desert eagle and the ear piece.
 * Never sweats in any heat. No voice inflection. Conveys an attitude of smug superiority and general contempt for mankind. Stiff and humorless personality. And he creepily materializes out of thin air.
 * So that's why Morpheus went to Las Vegas: he wants to pump Catherine Willows for info!
 * This simply has to be canon. He even looks exactly like the agents did in the first movie, redheaded and extraordinarily pale despite living in a constantly sunny locale.

Horatio Caine is in a coma or some other dream state, and CSI: Miami is his fantasy world.
What other possible explanation is there for the series's lionization of a guy who runs around acting like a major douchebag? The women want him; the kids all love and trust him despite his wrinkled face, unnatural speech, and creepy whispering. He's not a good personnel manager at all, but his entire team still worships him. Nobody he suspects of a crime is ever innocent. He makes a new dramatic mortal enemy every three days. He's basically the King of Miami; he can disbar lawyers within five minutes, murder people in cold blood with no consequences except for the ones that make him even 'more' badass, and hire and fire police detectives who don't even work in his department at will.

This also accounts for the complete absence of any real world physics or science and of people who aren't morons.

Expect the series to end with Horatio: waking up in a hospital bed, or his kid staring into a snowglobe, or his waking in his room with a beautiful woman in his shower, or with him splattering onto the Arctic snow.

Horatio Caine is none other than Jack Thompson
Think about it: he doesn't like video games, acts like he's Batman, and thinks everyone wants him dead.

The CSIs are serial killers.
They are way too successful and encounter way too many murders. And way too often, there turns out to be a connection between them and the crime. The secret is obvious: THEY are the perpetrators. Being CSIs gives them the perfect cover to manipulate the evidence and show off implausible 'enhanced' computer mockups to demonstrate their preplanned stories. Ecklie's the only clean CSI, and he has his suspicions. The series is from the perspective of their defense testimony.
 * Wait, wait, if that's the case, then how do you explain the events from "Grave Danger"?
 * Someone had a feud with the CSIs because they jailed his relative. Or there's more than one group of assassins in town.

Comic Books of CSI: Miami are on sale elsewhere in the CSI Verse
CSI: Miami is set in a comic book world. That means there must be comic books of it. If we're lucky, they'll reach the real world, and we'll soon see them tucked near Buffy Season 8 and Angel season 6... Or is that if we're unlucky?
 * It's already happened.

Brass is a reptilian shapeshifter.
The woman from the Lizard Cult was not hallucinating that snake-tongue. There really is a conspiracy of alien reptiles in the CSIverse.

It explains the more advanced technology.

The reason CSIs do so much multitasking fieldwork, interviews, and interrogations is that the Las Vegas lab is a training/recruiting center for The Men in Black that cover up this secret. Grissom leaves the lab because he's been recruited. Ecklie's in on the secret; his usual actions are Obfuscating Dickery.

Horatio Caine is the Smoke Monster from Lost.
Like the Island, CSI-verse Miami is only tangentially related to reality. Horatio and the Smoke Monster both live in hot, tropical environments but choose to dress in black. They are arbiters of justice via death.

Caine can get to any crime scene, bad guy's lair, etc. because he can transform himself into the black cloud.

They surround themselves with people who, given their emotional and physiological problems, shouldn't be allowed access to scissors, never mind handguns and rifles.

Finally, Horatio, being of non-human origins, doesn't have human emotions and can only make odd, unrealistic, unconvincing approximations of them.

Horatio Caine is Dexter of Dexter's Laboratory all grown up.
And he wants to get revenge on all the people he doesn't like MIT SCIENCE!!!!
 * He's also Dexter Douglas from Freakazoid, Dexter Morgan from Dexter, and Benjamin Poindexter from Ultimate Daredevil.

CSI takes place in the same universe as Criminal Minds
Because it would be awesome to see Horatio Caine or Ecklie be the victim of a Hotchalanche.
 * With the appearance of Angela's dad on Miami, it's also part of the Bones universe.

Nick killed the babysitter that raped him when he was a little kid
Nick has only mentioned that he was raped once, to Catherine in the second season. This makes sense because it was a traumatic experience; there was no need to bring it up for some seasons after.

Many years later, in an episode called "Death and the Maiden," a boy was raped. Even though Nick took the lead in the case, he never mentioned that he was raped, even though it would have been beneficial to do so at several points. But he did say, "If I were Tommy, I'd of killed him too."

He was in a similar position to Tommy once. Therefore, Nick did kill that babysitter. He did not bring up the rape during this case because he was afraid people would finish the parallel.

The Next Season of CSI will end with...
Catherine and Vartann's marriage. Because we deserve a little happiness, dammit!
 * Er, nope...we're pretty sure of that even though her end hasn't aired yet.

Viewers aren't morons ... but CSIs are.
Why is it relatively easy for us to figure out who the killer is before the CSIs do? We're supposed to.

The CSIs are so dependent on where the evidence takes them that they miss the things that the viewers are meant to catch.

There will be another spinoff to cover another area of the country, again.
There are is one team in the west (Vegas), southern coast (Miami), and the Northeast (NYC). Other possibilities:
 * 1) Los Angeles. It's where all the cool large procedural agencies have branches. NCIS is there, LA Law was there, Law and Order LA was there—even Columbo was there. But that might be a bit close to Las Vegas...
 * 2) Washington, DC. A coastal city, perhaps a little close to NYC, but it would be fun. Or maybe Baltimore—that is another popular place for procedurals.
 * 3) Indianapolis...
 * 4) Rochester, Minnesota.
 * 5) Rochester, New York. If Los Angeles would work, so would this.
 * 6) Chicago. Lots of shows there, but few criminal procedurals, and we want something more uplifting than The Chicago Code.
 * 7) Dallas. One in Texas would make a nice genre change—dragging police work into the 22nd century...
 * 8) Louisville, Kentucky. Much bigger and darker than it looks on Derby Day. May have some of the benefits of Dallas.
 * 9) Detroit!
 * Or maybe another country? Law and Order has a UK version, so why not CSI too? Or would The BBC sue them for copying Waking the Dead?

The gorilla in "Evaluation Day" came from the same zoo as the grizzly in "Unbearable"
And was also the victim of a "canned hunt". Why else would some furtive kill and skin a gorilla in Vegas?

== Thumpy G (Revenge is Best Served Cold) was actually Det.Danny Messer from NY's crime lab, taking part in an undercover mission. He just didn't say it to the CSIs so as not to break his cover to anyone else around them. ==

D.B's wife will be played by Shelley Long
At the moment it looks like his wife is The Ghost, just mentioned a lot but not seen. However it seems like since D.B is well known to audiences as Sam from Cheers then it wouldn't be much of a suprise to have the one who played Diane on that show. This is based on genre-saviness because Tropes Will Ruin Your Life.