Perplexing Potential Prisoners

First of all we will create a table showing all the possibilities for the identities.

$\begin{array}{c|c|c|c|c|c} \text{Aaron} & \text{Brendan} & \text{Cynthia} & \text{Derek} & \text{Esther} & \text{Fabio} \\ \hline \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} \\ \text{Accomplice} & \text{Accomplice} & \text{Accomplice} & \text{Accomplice} & \text{Accomplice} & \text{Accomplice} \\ \text{Criminal} & \text{Criminal} & \text{Criminal} & \text{Criminal} & \text{Criminal} & \text{Criminal} \end{array}$

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Now look at Aaron's and Fabio's statements. Since Aaron says he's a citizen, this rules him out of being the criminal (as the criminal is the only one who wouldn't be able to say this). Fabio's statement means that he must be a citizen - think about this.

$\begin{array}{c|c|c|c|c|c} \text{Aaron} & \text{Brendan} & \text{Cynthia} & \text{Derek} & \text{Esther} & \text{Fabio} \\ \hline \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} \\ \text{Accomplice} & \text{Accomplice} & \text{Accomplice} & \text{Accomplice} & \text{Accomplice} & \text{} \\ \text{} & \text{Criminal} & \text{Criminal} & \text{Criminal} & \text{Criminal} & \text{} \end{array}$

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Now look at Brendan's and Cynthia's statements. Let us assume that Cynthia is the accomplice. This means that she is lying so Brendan is not a citizen (and hence must be the criminal as Cynthia is the accomplice). However Brendan's statement would then be truthful, and he says that the robbery was not a combination of him and Cynthia, creating a contradiction. This means that Cynthia isn't the accomplice, so she is telling the truth and Brendan is therefore a Citizen.

$\begin{array}{c|c|c|c|c|c} \text{Aaron} & \text{Brendan} & \text{Cynthia} & \text{Derek} & \text{Esther} & \text{Fabio} \\ \hline \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} \\ \text{Accomplice} & \text{} & \text{} & \text{Accomplice} & \text{Accomplice} & \text{} \\ \text{} & \text{} & \text{Criminal} & \text{Criminal} & \text{Criminal} & \text{} \end{array}$

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Now look at Derek's and Esther's statements. Esther cannot be the criminal (since anyone accusing anyone else of being the criminal cannot be the criminal - think about this).

$\begin{array}{c|c|c|c|c|c} \text{Aaron} & \text{Brendan} & \text{Cynthia} & \text{Derek} & \text{Esther} & \text{Fabio} \\ \hline \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} & \text{Citizen} \\ \text{Accomplice} & \text{} & \text{} & \text{Accomplice} & \text{Accomplice} & \text{} \\ \text{} & \text{} & \text{Criminal} & \text{Criminal} & \text{} & \text{} \end{array}$

Let us assume that Esther is a citizen so is telling the truth. Since she says the criminal is Aaron, Cynthia or Fabio, the criminal must be Cynthia and there are two possibilities for Derek.

• If Derek is a citizen, then his statement is true and the robbers stand next to each other, but this can't happen as Derek is a citizen.
• If Derek is the accomplice, then his statement is false and the robbers don't stand next to each other, but this is a contradiction since it is Cynthia and Derek.

This means that we always get a contradiction, so our initial assumption that Esther is a citizen is wrong, and Esther is the accomplice . Since she is lying, the criminal is not Cynthia, so the criminal is $\boxed{Derek}$ , which can be checked to hold true with Derek's true statement about the robbers next to each other (as well as every other statement)

Aaron claims to be a citizen, so he can not be the criminal. Brendan says it was not Cynthia and him. Cynthia says he is a citizen. If this is true, she could be the criminal or a citizen. If it is not true, then she is the accomplice and he is not a citizen(and she is the accomplice) so he would be the criminal. But the criminal would tell the truth! This forms a contradiction, hence Cynthia is not the accomplice and her statement of Brendan being a citizen is true.Also, it then makes sense that Brendan’s statement is true, as a citizen can not do the robbery. Derek than claims that the accomplice and criminal are next to each other. This doesn’t have to be true(obvious case of a contradiction if Cynthia is the criminal), but it is far better to evaluate this in regard to Ester’s statement. She claims it was Fabio, Aaron(who we know is innocent) or Cynthia. However, can Cynthia be the criminal? Brendan is innocent so, according to Derek, his statement is true and he is thus the accomplice. If his statement is a lie, he is not the accomplice, but if it is the truth, he is the accomplice. This is a contradiction. So if Ester’s statement is true, Fabio is the criminal. This forms two contradictions: one similar to Cynthia being the criminal(look back at Derek’s statement) and the other(which may be easier to observe) is that only a citizen can claim not to be a criminal, as the criminal would be lying and the accomplice telling the truth. Either way, Ester is lying and thus the accomplice. Derek’s statement is thus true, so the criminal is either Derek or Fabio(who we know to be innocent). Hence Derek is the criminal with Ester as the accomplice.

"The seasoned criminal will also tell the truth as their experience will cause them to play it safe", so the criminal can't claim to be an innocent citizen. Thus, Aaron cannot be a criminal.

Overall, there's only one lie among the six statements. By Brendan's "Cynthia and I didn't perform the robbery together", either he's really innocent or Cynthia told the truth. Anyway, both options leading to an innocent citizen Brendan.

Derek : The criminal and the accomplice are standing next to each other.
Esther : The criminal is Aaron, Cynthia, or Fabio.
Fabio : I'm not the murderer.

So the sole lie has to be one of the above. Let's look at Esther's bold accusation first. Aaron is innocent, so if neither Cynthia nor Fabio is the criminal, then Esther is the accomplice (with the last suspect left, Derek as the criminal). As for Derek, either he's telling the truth or Derek's an accomplice to a criminal Fabio. Anyway, Cynthia can't be an accomplice while Esther can't be a criminal. Now I'm convinced that this problem needed more clarification to clear Fabio of any crime.

Suppose Fabio is lying, then he must be the accomplice and Esther another liar (with all 3 names she mentioned couldn't have been the criminal), so we can rule this one possibility out. So either Derek or Esther is the lying accomplice. If Derek is accomplice, then the criminal would be Fabio. If Esther is accomplice, then the criminal would be Derek.