By Rachel Harvey
BBC News, Bangkok
The whereabouts of the stolen blue diamond is a mystery
A 20-year crime mystery that has seriously affected diplomatic relations between Thailand and Saudi Arabia has taken another twist.
Five Thai police officers have been charged with the murder of a Saudi businessman who disappeared in 1990.
The case stems from the theft of millions of dollars of jewels from a Saudi palace by a Thai man employed as a janitor in 1989.
All five suspects deny the murder charges.
The case of the jewels, the janitor, the palace and the police has been a source of intrigue and diplomatic tension for two decades.
First there was the theft - $20m (£12.5m) worth of jewels, including a very rare blue diamond, taken from a Saudi palace and smuggled into Thailand in 1989.
The thief was caught and much of the jewellery was recovered.
But most of what was returned to Saudi Arabia turned out to be fake.
The following year, three Saudi diplomats in Thailand were murdered and a Saudi businessman, Mohammad al-Ruwaili, disappeared.
The five policemen who have now been charged are accused of abducting and killing Mr Ruwaili. His body has never been discovered.
One theory is that his death was the result of an interrogation that went badly wrong.
The theft and subsequent murders soured relations between Thailand and Saudi Arabia.
Thousands of migrant Thai workers lost their jobs and billions of dollars in trade have been sacrificed.
Tuesday's decision may go some way to improving the situation.
But the murders of the diplomats remain unsolved, and the whereabouts of the real jewels - including the famous blue diamond - remain a mystery.