The police photograph of Vincenzo Peruggia.

If you are going to steal something, then the Mona Lisa sounds like a crazy idea. It might be worth millions, but it is also very easily identified and very well guarded. But it was stolen once:

On 21 August 1911, Louis Béroud, a painter, went to the Salon Carré in the Louvre where the Mona Lisa had been on display for five years. The Mona Lisa was always there - in between Correggio's Mystical Marriage and Titian's Allegory of Alfonso d'Avalos. All he found were four iron pegs.

Things were a little more lax back then. Béroud contacted the section head of the guards, who thought the painting was being photographed. The photographers knew nothing of it. The Louvre was closed for an entire week as the theft was investigated.

French poet Guillaume Apollinaire, who had once called for the Louvre to be "burnt down", was arrested on suspicion of the theft. His friend, the now famous artist Pablo Picasso, was brought in for questioning, but both were later released. At the time, the painting was believed lost forever.

Two years later, Louvre employee Vincenzo Peruggia grew impatient.  He was caught trying to sell the Mona Lisa to a Florence art dealer. Having spent two years in Peruggia's apartment, it was exhibited all over Italy before being returned to the Louvre in 1913.

Peruggia had stolen it simply by entering the building during regular hours, hiding in a broom closet and walking out with it hidden under his coat after the museum had closed.

The con-man, Eduardo de Valfierno, had master-minded the theft. He had commissioned the French art forger, Yves Chaudron, to make copies of the painting to be sold as the real thing. But he didn't need the original for his con. He just needed it to be missing. De Valfierno never contacted Peruggia again after the crime.

But Peruggia became impatient and made the fatal mistake of trying to sell his treasure. The Mona Lisa is back, the crime solved and the criminals identified. Just as it should be.

Brian Lane, in the introduction to his Chronicle of Murder* lists seven motives which he feels covers all murders. The same list could probably be applied to all crimes. It is:

* Gain - to acquire financially valuable objects, inheritance or money by some other means, or possessions of sentimental value.
* Jealousy - this takes a wide range. Not just romantic, people are also jealous of possessions and status.
* Revenge  - perceived wrongs can be extremely strong motivators. This theme is widely used in crime fiction.
* Elimination - eliminating someone for hate or because they are in the way of some crucial goal. They don't have to be killed!
* Lust - sexual attraction is a strong motivator, but probably not a good idea as a motive for a young writer.
* Conviction - religious, moral and other strong convictions and beliefs have spurned a myriad of crimes over the centuries.
* Pure Thrill - the thrill of doing something which is wrong and getting away with it. Vandalism falls into this category - but then so can almost anything else.

When you create your criminal, he or she must have a strong motive for committing the crime, or the story will be flat. Your criminal must be consistent with the crime, the era and the nature of the situation. For example, if you are considering using fire arms in a historical mystery, then be aware that Samuel Colt made the first firearm available to the general public, and therefore available to the criminal, in 1847. Crimes set in times prior to that should not have the criminal whip out a gun.

Your criminal must have:

Create your criminal - the one who will commit your crime.

Ensure you get to know your criminal. Understanding his or her thinking is crucial to writing a good crime mystery. One way to get to know any character is to interview them.

Questions to ask your criminal character:

* Lane, Brian, 2004, Chronicle of Murder: a dark and bloody history of our age, Constable & Robinson, London.