Atefeh Rajabi in her last moments

It was exactly 6am and the start of another blisteringly hot summer day when 16-year-old Atefeh Rajabi was dragged from her prison cell and taken to be executed.

Every step of the way the troubled teenager plagued by mental problems shouted "repentance, repentance" as the militiamen marched her to the town's Railway Square.

The Iranian judge who had sentenced Atefeh to death was left unmoved as he personally put the noose around her neck and signalled to the crane driver.

Kicking and screaming, Atefeh was left dangling for 45 minutes from the arm of the crane as the crowd sobbed and - under their breath - damned the mullahs.

Atefeh's crime? Offending public morality. She was found guilty of "acts incompatible with chastity" by having sex with an unmarried man, even though friends say Atefeh was in such a fragile mental state that she wasn't in a position to say no.

But Judge Haji Rezaii was determined she should hang, regardless of the rules of international law which say only adults over 18 can be executed, and that the courts have a duty to children and the mentally ill.

The brutal end to Atefeh's short life has shone a new light on Iran's Shariah law, where adultery, theft and rape all carry the same punishment - death. Officially around 100 people - some just children like Atefeh - are executed each year. But human rights groups say the true figure could be much higher in a country where only half of the women can read, only one in 10 have a job and two-thirds are beaten in their homes.

Life was never easy for Atefeh, who was brought up in the industrial town of Neka, 250 miles from Tehran and close to the Caspian Sea. Her mother died when she was a child and her father Ghasseem, a heroin addict, left her grandparents to bring her up. She suffered from bi-polar disorder, which led to severe mood swings from hyperactivity to depression. Worried parents told their children to stay away from her - something many regret now. "Perhaps we should have helped her instead," said Hamid. "I think the death of her mother had a devastating effect. Before that, she was a normal girl. Her mother was everything to her. After she died, there was no one to look after her."

Mina, a childhood friend, said Atefeh was abused by a close relative. "She never dared talk about it with an adult," said Mina. "If she had told her teacher they'd have called her a whore. Tell the police? They lock you up and rape you." Atefeh first appeared in court, accused of having sex with an unmarried man at 14. Over the next two years she was accused of the same crime with different men.

They denied it and were sentenced to the lash and then released. But Atefeh pleaded guilty and each time received 100 lashes and a prison term. Mina said: "Atefeh sometimes talked about what these 'moral' Islamic policemen did to her while she was in jail. She still had nightmares about that. Atefeh said her mood swings made it easy for men to take advantage of her, and that most of her lovers were in the security force."

Two of them were members of the anti-vice militia. They encouraged other men to sign statements saying Atefeh had engaged in vice, and even claimed she had AIDS.

It was when Atefeh appeared before Judge Rezaii for a fourth time that she lost her temper - and also her life. In a rage she tore off her hi jab - a headscarf - and told the judge she had been raped and it was his duty to punish her tormentors, not their victim.

Rezaii told her she would hang for her "sharp tongue" and that he would put the noose around her neck himself. It became a personal crusade as he travelled to Tehran and convinced the Supreme Court to uphold his verdict.

Two petitions by her friends, saying she was mentally unwell, were ignored. Her father produced her birth certificate proving she was 16. Yet the judges "decreed" she was 22.

Atefeh also wrote to the Supreme Court: "There are medical documents that prove I have a weak nerve and soul. In some minutes of the day and night I lose my sanity. In a society where an insane person can be serially raped it is no wonder that a person like me is the victim of such an ugly act."

The day before she died she wrote again, saying: "Repentance, repentance, repentance." In Iranian law anyone who shows remorse has an automatic stay of execution and a right to appeal, but she was ignored.

A local pharmacist watched Atefeh's execution on August 15, 2004. "She looked so young standing there," he said. "Rezaii must have felt a personal grudge against her. He put the rope around her neck himself. I looked around and everyone in the crowd was sobbing and damning the mullahs." The family's lawyer has now filed a suit of wrongful execution against the judge and is preparing a murder case. Her life is also the subject of a secretly filmed documentary, Execution of a Teenage Girl, which will be screened on BBC2 on Thursday.

One of Atefeh's teachers said the authorities wanted to make an example of her: "She wouldn't take injustice from anyone, but the mullahs equate these qualities in a girl to prostitution and evil. They wanted to give all the girls and women a lesson."

Amnesty International UK director Kate Allen said: "The killing of Atefeh is a catalogue of the most appalling human rights violations. The public hanging of a child, believed to be mentally incompetent, totally beggars belief. To hang a child flies in the face of all that is humane."

SHARIA LAW PENALTIES imposed by Iran's religious mullahs include:

THEFT: Amputation of hands or feet for persistent offenders.

ADULTERY: Death by stoning.

UNMARRIED SEX: 100 lashes.

CONVERSION TO RELIGION OTHER THAN ISLAM: Death.

SODOMY: Death for adults, 74 lashes for consenting child.

LESBIANISM: 100 lashes, or on the fourth occasion death.

HOMOSEXUAL KISS: 60 lashes.

RUBBING ANOTHER MAN'S THIGHS OR BUTTOCKS: 99 lashes - on 4th occasion, death.

ALTERING THE NOSE OF THE PRESIDENT USING PHOTOSHOP: Death.

Iranian President Mahmoud Ahmadinejad: "Yeah, we hanged her good!"