logical deduction - A Space Station 13 tricky situation

You are the Captain of the Space Station 13, and everything went bad very quickly. Most of the crew died, and it took you not so long to figure out that some people are not who they're supposed to be (hence the bloody mess). Your task is to find out who is who in order to prevent the bad guys from reaching the escape shuttle.

There are 8 other crewmen with you : the Security Officer, the Medical Doctor, the Chief Engineer, the Cook, the Cargo Technician, the Botanist, the Janitor and the Clown (every station needs a Clown). You know that 4 of them are innocent, and that the 4 others are a Traitor, a Changeling, a Cultist and a Space Wizard. You also know for facts that:

• Everybody knows who is who (well... except you, the Captain, which is quite a shame).


• The only exception to the previous fact is that nobody knows who is the Changeling (except himself of course), and everybody believes the crewman the Changeling is impersonating is innocent.


• All innocent crewmen say the truth, or what they believe is the truth.



• The Cultist also says the truth (or what he believes is the truth), as part of a complicated ritual to summon N̻͔͓̳͇͖̝͠a̲͙̟͓̐ͧ̇̍̈ͥ̚͜r̲̠͇̲͈̐-͙̜͕̪͕͓͍̒̎̀S͈͕̅̾̕ͅi̙͋̎̒ͣ͗e̱͋̈́.


• The Traitor, Changeling and Space Wizard all lie (or what they believe is a lie).


• The Space Wizard will put a curse on you after you interrogated him, making you think the next crewman you interrogate said the opposite of what he actually said. For example, if you hear the crewman you interrogate just after the Space Wizard saying "The Janitor is a Cultist", what he actually said was "The Janitor is NOT a Cultist".

And this is what everyone said to you (in order of interrogation):

Security Officer: "The Medical Doctor is innocent."

Chief Engineer: "The Botanist is not innocent..."

Janitor: "The Clown is a Space Wizard!"

Cargo Technician: "The Chief Engineer is a Cultist!"

Medical Doctor: "The Cook is a Changeling!"

Clown: "The Janitor is a Traitor!"

Botanist: "The Security Officer is innocent."

Cook: "The Cargo Technician is a Traitor!"

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Remember, your goal is to assert the identity of everyone, not just sort bad guys and innocents. The Traitor must be shot in the head, the Changeling burnt to ashes, the Cultist spaced and the Space Wizard properly dismembered.

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_{If you liked this puzzle, try the rest of the story!}

Answer

Traitor: Janitor, Changeling: Cook, Cultist: Botanist, Space Wizard: Cargo Technician

The rest is innocent. Explanation:

First, observe that there are three people lying and five speaking the truth. Depending on where the Space Wizard is, two to four people's statements are false, the rest is true. For simplicity's sake, I assume all crew members are male.
The Medical Doctor's statement is false, so either (1) the Cargo Technician is the Space Wizard and the Medical Doctor is either innocent or the Cultist, or (2) the Cargo Technician is not the Space Wizard and the Medical Doctor is guilty but not the Cultist. We'll see that (2) leads to a contradiction.
In case (1) the Cook lies and must be the Changeling or the Traitor. If he's the Traitor, the Clown lies and must be the Changeling. Then the Janitor also lies, which is impossible since we've already identified three lying crew members.
So the Cook is the Changeling. Now, if the Clown lies, he must be the Traitor himself. Everybody else speaks the truth, including the Cargo Technician, who claims the Chief Engineer is the Cultist, but then the Botanist is not innocent and must be lying, which is a contradiction.
So the Clown speaks the truth, the Janitor is the Traitor and everybody else speaks the truth. According to the Chief Engineer, the Botanist is the last guilty member; he must be the Cultist. You can check that the other statements are now true as well.

Case (2) leads to a contradiction: the Medical Doctor lies, so he's guilty and the Security Officer lies as well. The Botanist's statement is false, so the third (and last) lying member is either the Botanist himself (a) or he lies because the Clown is the Space Wizard (b) making him the third lying member.
Now if the Cook speaks the truth, the Cargo Technician would be the fourth lying person which is impossible. So the Cook's statement is false because the Botanist is the Space Wizard, but then the Janitor is also lying, which leads to a contradiction.

It's a ... tricky situation ... to explain; I might have made some mistakes and used 'lying/speaking the truth' where I meant 'statement is false/true' or vice versa. Captain Glorfindel out.