Who stole the cake?

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?

 

Answer:

Charlie committed the terrible crime.
Looking at Brian's statements, one of the statements was a lie and the other was the truth. Therefore it must have been either Charlie or Edward.
Looking at Derek's statements, for the same reason, it was either Charlie or Brian.
Therefore it must have been Charlie who committed the crime. Double checking this against the other statements confirms this.