The Vatican has for the first time opened its own investigation into the case of Emanuela Orlandi, a 15-year-old Vatican citizen who disappeared in the summer of 1983.

The Orlandi family's lawyer Laura Sgro confirmed the probe, saying: 'The secretariat of state has authorised the opening of an investigation into a grave in the Teutonic Cemetery inside the Vatican.'

It follows an anonymous tip-off which advised Sgro to 'look where the angel is pointing'.

The letter to Sgro also included a photograph of the tomb that features a marble angel holding a tablet reading 'Rest in Peace' in Latin.

Protesters hold posters with Emanuela Orlandi's image calling for 'truth and justice' for the 15-year-old who vanished in 1983, in a demonstration in St Peter's Square in 2012

The Vatican opened its own investigation after an anonymous tip-off which advised Emanuela Orlandi's family lawyer Laura Sgro to 'look where the angel is pointing'. The letter to Sgro also included a photograph of the tomb that features a marble angel holding a tablet reading 'Rest in Peace' in Latin (pictured)

The tombstone is inscribed with a dedication to a German prince who was nominated archbishop by Pope Pio IX in 1857, and his wife.

Tests done on the tomb since the tip-off show that it has been opened at least once, and the date of the tablet is different to that of the tombstone, according to Italy's Corriere della Sera daily.

Sgro said she had also been able to 'verify that some people knew there was a chance Emauela Orlandi's body had been hidden in the German cemetery,' her letter to the Vatican read.

People had also been leaving flowers on the tomb, she said.

A poster calling for information on Emanuela Orlandi, who disappeared aged 15 from a Rome street in 1983

The Vatican had previously said it was handling a request from the Orlandi family to reopen the grave.

'I can confirm that the letter by Emanuela Orlandi's family has been received... and the requests it contains will be studied,' Vatican spokesman Alessandro Gisotti said in a statement.

Interim Vatican spokesman Alessandro Gisotti declined further comment.

Emanuela was the daughter of a Vatican employee who lived with his family in the tiny city state.

She was 15 when she disappeared after a music lesson in Rome.

The family have long demanded to see Vatican documentation about the enduring mystery.

The cold case attracted fresh attention at the end of October when two sets of remains were found in the basement of the Vatican Nunciature, an extraterritorial Church property located in Rome's city centre.

The identification of at least one of the bodies as female led to immediate speculation in Italy that the findings might eventually shed light on one of the country's most persistent mysteries.

Investigators said at the time that preliminary examinations of the bones indicated they belonged to a woman probably in her thirties.

But, despite the estimation of bones' age, the Orlandi family lawyer said they would wait for DNA results.

The Vatican has opened an investigation into the 1983 disappearance of 15-year-old Emanuela Orlandi. An anonymous tip-off had previously claimed that the body is inside an angel-fronted tomb in a cemetery in the Vatican (pictured)

The Orlandi family's lawyer Laura Sgro confirmed that the Vatican has 'authorised the opening of an investigation into a grave in the Teutonic Cemetery inside the Vatican'. The cemetery is pictured from the dome of St. Peter's Basilica

One hypothesis for Emanuela's disappearance is that she was not killed immediately but instead held for years against her will.

Investigative sources, however, told Italian media in the following weeks that the bones were too old to be related to the Orlandi case.

For more than 35 years, Italian media have been obsessed with the fate of Emanuela.

Over the years, many rumours have swirled about what happened to her.

According to some theories, the teenager was snatched by an organised crime gang to put pressure on Vatican officials to recover a loan.

Another claim was that she was taken to force the release from prison of Mehmet Ali Agca, the Turk who attempted to assassinate Pope Jean Paul II in 1981.