A murder case that has obsessed India for four years came to court on Friday when a middle-class couple from Delhi stood trial on charges of killing their teenage daughter and domestic servant.

At first police blamed the servant for murdering Aarushi Talwar, 13, but now her parents are accused of stabbing them both to death in a case awash with sexual rumour, as well as charges of police incompetence and a media witchhunt.

Rajesh and Nupur Talwar, who are successful dentists, have always denied killing their daughter and Nepalese employee Hemraj Banjade in the capital's suburb of Noida in May 2008.

The murders have raised awkward questions about the relationship between newly-wealthy Indian families and the poor, often-migrant servants who cook, clean and look after their every need at home.

When Aarushi was found with her throat slit, police immediately said Hemraj had murdered her - triggering a media firestorm that tapped into fears within many Indian households about untrustworthy domestic staff.

But almost two days after Aarushi was killed, officers found Hemraj's body lying in the hot sun on the roof terrace of the house after he was apparently murdered at the same time as Aarushi.

The discovery kicked off fevered speculation about whether her parents had killed the two after discovering their daughter was in a relationship with the servant, or that they were killed to hide the parents' alleged affairs.

“Our stand was that the probe of the investigating officer proves that no outsider was involved in this,” Central Bureau of Investigation (CBI) counsel R.K. Saini told reporters after the decision to prosecute for murder.

“Circumstantial evidence is pointing out that whatever has been done, the parents only have done it,” he said.

But major doubts have arisen over the case - not least how the police failed to gather forensic evidence properly from the scene and the way that they reversed their stance to say that they had proof of the parents' guilt.

The CBI even closed the case last year declaring it unsolved, before a sudden U-turn in favour of a prosecution.

The investigative magazine Tehelka has been especially critical of the police work and condemned what it called the “conspiratorial hysteria” fuelled by media coverage of the case.

“The Talwars have been pulled through some of our society's darkest anxieties,” the magazine said. “Dante's hell is alive in Delhi and the Talwars seem to have no way out of it.”

In a television interview last year, Nupur Talwar said she and her husband had been the victims of unsubstantiated gossip, innuendo and police scapegoating.

“I have almost lost faith in humanity,” Talwar said. “I was a believer in truth and justice... I always thought truth would prevail in the end, but I'm not so sure about that now.”

One of the Talwars' supporters has been Patrick French, a British author who undertook his own study of the murder for his 2011 book on contemporary Indian issues.

“It makes no sense to say that they did or would have killed their daughter,” he told AFP, adding he was “100 percent convinced” of their innocence.

“If you are looking for a motive you are left with these bizarre theories that the police have come up with suggesting a relationship between Aarushi and Hemraj for which there is not a jot of evidence,” he said.

India's newspapers often recount grisly murders but the Aarushi case has generated unprecedented interest.

“It sheds a light on police inefficiency and corruption, the middle-class fear of servants, and every parent's terror of their child being killed,” said French.

The trial is being held without a jury as in all Indian courts in the town of Ghaziabad on the outskirts of New Delhi.

On Friday, the judge heard demands from the Talwars' laywer that they be given access to more police statements and other information related to the investigation, reports said.

The judge set the next hearing for Monday. - Sapa-AFP