Stealing the Mona Lisa
On the morning of August 21, 1911, Louvre officials discovered that the Mona Lisa was gone; it's usual spot on the wall was vacant. The crime was committed by three Italian handymen who had hidden in a closet all night and waited until the morning before the museum opened to steal the painting. Unsurprisingly, many people at the Louvre were fired and France went into mourning. The main suspect Vincenzo Perugia, who was captured in Italy about two years later, stole the painting because he thought it belonged to Italy. He only spent a few months in jail because people hailed him as a patriot.
The mystery to be solved is "Where is the Mona Lisa, if it is even still intact, and how can the police find it?"
The victim is the Louvre Museum and the country of France as a whole.
At first Pablo Picasso and his friend Guillaume Apollinaire. However, the main suspect and the actual perpetrator was Vincenzo Perugia.
Basically none, other than the fact that the wall was bare. This is the reason why Perugia was not captured until about two years later; there was nothing to go off of.
The Proposed Narrator
The narrator will probably be some sort of detective/inspector that was assigned to the case.