Cake Theft Puzzles

During a recent police investigation, Chief Inspector Stone was interviewing five local villains to try and identify who stole Mrs Archer's cake from the mid-summers fayre. Below is a summary of their statements:

Arnold:  it wasn't Edward
         it was Brian

Brian:   it wasn't Charlie
         it wasn't Edward

Charlie: it was Edward
         it wasn't Arnold

Derek:   it was Charlie
         it was Brian

Edward:  it was Derek
         it wasn't Arnold

It was well known that each suspect told exactly one lie. Can you determine who stole the cake?

Ans:: 

Charlie committed the terrible crime. The way to solve this puzzle is to look at each clue. We know that exactly one of each person's statements is true. Looking at Arnold's statements, let's check to see 'it was Brian' is true? If 'it was Brian' is true, then we know the other statement is false, therefore it was Edward. This is a contradiction. Hence we now know it wasn't Brian, nor Edward (as 'it wasn't Edward' must be the true statement). Looking at Charlie's statement, we can similarly determine that it wasn't Arnold either. Edward's statement gives us that it wasn't Derek, which leaves only Charlie as the culprit. It is always wise to check this against the other clues. QED.

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