Is this right- Derek said: Duke was an idiot
Or this- Derek said Duke was an idiot
Or this- Derek said: "Duke was an idiot"
Or this- Derek said "Duke was an idiot"
Plz help me, im writing a book, and I got serius problems with that.

Derek said, 'Duke was an idiot'.

Shouldn't the period be inside the closing quote? The spoken sentence is complete and grammatically well formed.