The trial has started in Iran of two men accused of murdering 17 children, two men and a woman in the desert outside the country's capital, Tehran.
By Frances Harrison
BBC correspondent in Tehran
Iranian state media said seven others would go on trial later, accused of sexually abusing the children.
At least 16 police are being reprimanded or referred to the judiciary for incompetent handling of the investigation into the killings.
If found guilty, the two accused face the death penalty.
The Iranian media called the alleged killers the 'scavengers of the Tehran desert'.
The two men worked in the brick kilns on the outskirts of the capital.
They are accused of luring children into the desert, stunning them with blows from a large stone, abusing them and then shattering their skulls.
The killers would bury the children in makeshift graves and then leave a dead animal on top to disguise the smell.
The murders took place over a period of more than a year.
One Iranian paper reported that many of the victims were illegal Afghan refugees whose parents were reluctant to file complaints with the police for fear they would be deported - hence the delay in investigating the killings.
'Pain and humiliation'
At the start of the hearing the coroner confirmed that the accused were sane enough to stand trial.
The authorities say they decided to hold the trial behind closed doors to spare the families further pain and humiliation.
But some newspapers in Iran have criticised the decision, saying the media should play an important role in curbing such crimes by keeping people informed.