logical deduction - A Criminal Conspiracy (Who Is Guilty #4)

[Appeal: I'm trying to figure out a fun puzzle formula. There are many out there ("Who owns the fish", sudoku, etc). I'm interested in feedback on whether this works or is interesting for people. Possible to solve by hand. Techniques you found helpful, etc. Also a rating for this if you solve it: Easy; Tricky; Difficult; Fiendish]

After a long hiatus, you are back on the case. You arrive on the island to find a dead body and a number of possible suspects. You separate them and take their statements.

This is what you know from all those training sessions at the academy:

1. Guilty people sometimes lie and sometimes don't.



2. Guilty people will always say their co-conspirators are innocent (if they mention them).


3. Innocent people tell the truth (when they know it).


4. Except for when they make up a statement to try to impress you. But they never make up more than one statement.


5. The smallest conspiracy that is consistent with the statements is the answer.

Suspect Names: Barbara, Donnie, Jackeline, Luisa, Mauricio, Roy, Shakia, Terence, Vanessa.

Statements of Barbara:
- I am innocent
- Roy is innocent

- Vanessa is innocent
- Shakia is innocent

Statements of Donnie:
- I am innocent
- Luisa is innocent
- Terence is guilty
- Shakia is innocent

Statements of Jackeline:
- I am innocent
- Shakia is innocent

- Luisa is innocent
- Terence is innocent
- Vanessa is guilty

Statements of Luisa:
- I am innocent
- Mauricio is innocent
- Shakia is guilty
- Donnie is guilty
- Jackeline is innocent

Statements of Mauricio:

- I am innocent
- Roy is innocent

Statements of Roy:
- I am innocent
- Mauricio is innocent
- Terence is guilty

Statements of Shakia:
- I am innocent
- Barbara is innocent
- Donnie is innocent

- Terence is guilty
- Roy is guilty

Statements of Terence:
- I am innocent
- Vanessa is guilty
- Mauricio is guilty
- Jackeline is innocent
- Donnie is innocent
- Shakia is guilty

Statements of Vanessa:

- I am innocent
- Donnie is innocent
- Mauricio is innocent
- Barbara is innocent
- Terence is innocent

Here's a table summarizing all the information:

Statements     | B | D | J | L | M | R | S | T | V | 
----------------------------------------------------
Barbara        | I |   |   |   |   | I | I |   | I |

----------------------------------------------------
Donnie         |   | I |   | I |   |   | I | G |   |
----------------------------------------------------
Jackeline      |   |   | I | I |   |   | I | I | G |
----------------------------------------------------
Luisa          |   | G | I | I | I |   | G |   |   |
----------------------------------------------------
Mauricio       |   |   |   |   | I | I |   |   |   |
----------------------------------------------------
Roy            |   |   |   |   | I | I |   | G |   |

----------------------------------------------------
Shakia         | I | I |   |   |   | G | I | G |   |
----------------------------------------------------
Terence        |   | I | I |   | G |   | G | I | G |
----------------------------------------------------
Vanessa        | I | I |   |   | I |   |   | I | I |
----------------------------------------------------

Answer

There must be 3 conspirators.

Let's start by looking at Terence. He has accused 3 people and 3 people have accused him.

If we make an initial assumption (Assumption#1) that he is innocent, then either (Assumption#2) has identified 3 guilty conspirators and one of his other statements may be a guess, or (Assumption#3) he has identified 2 guilty conspirators and incorrectly guessed at a third, in which case his other statements must be true.

Starting from Assumption#3:

Terence has declared that 2 other people are innocent, so we can mark them all as innocent.

We can now see that Donnie thought that Thomas was guilty. This was an incorrect guess, so Donnie's other statements must be accurate. We can now mark more people as innocent.

If we look at Luisa, we can see that she has incorrectly accused Donnie and Shakia. So Assumption#3 cannot be correct.

So let's try Assumption#2:

Terence has correctly identified 3 guilty people

These people would not have collared any of their co-conspirators, so we can now mark Roy as innocent.

But Roy has incorrectly accused Terence as guilty and incorrectly identified Mauricio as innocent, so Assumption#2 must be incorrect.

Now we have disproven Assumption#3 and Assumption#2, so Assumption#1 must also be incorrect.

This means that Terence must be guilty.

From this starting point

we can mark all the people he has accused as being innocent (as he wouldn't have named a co-conspirator).

Similarly, anyone that has accused Terence must be innocent too.

Now Luisa has accused 2 innocent people, so she must be guilty.

Shakia has incorrectly guessed about Roy, so her statement about Barbara must be true, making Barbara innocent too.

Which leaves Jackeline who has made 2 false statements, so she must be a conspirator too.

So the guilty people are:

Terence, Luisa and Jackeline

Interesting puzzle. As far as I can tell, rule number 5 is unnecessary in this case. It was straightforward enough to solve by hand without running into trouble - just making assumptions and disproving them to arrive at a unique solution. So I would rate it as Tricky just because of the need to disprove other possible solutions.