The Vatican has said it will open two tombs in a tiny cemetery on its grounds and test bone DNA to help solve the 36-year-old disappearance of a teenager.

The graves in the centuries-old Teutonic Cemetery will be opened on July 11 in front of the family of Emanuela Orlandi, after they received an anonymous tip that she might be buried there.

The family's lawyer Laura Sgro said they were grateful for the Vatican's decision.

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The graves in the centuries old Teutonic Cemetery will be opened on July 11 in front of the family of Emanuela Orlandi (right), after they received an anonymous tip that she might be buried there. Protesters hold posters with Emanuela Orlandi's image (left) calling for 'truth and justice' for the 15-year-old - who vanished in 1983 - during a demonstration in St Peter's Square in 2012

Orlandi's disappearance in June 1983, when she was 15, is one of the most enduring modern mysteries of the headquarters of the Catholic Church - and has been the subject of wild speculation by Italian media.

Unproven theories include an attempt to secure the freedom of a gunman jailed for trying to assassinate Pope John Paul II, and a connection to the grave of Enrico De Pedis, a mobster buried in a Rome basilica.

His tomb was opened in 2012 but nothing was revealed.

The Vatican opened its own investigation in April after an anonymous tip-off advised 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). Ms Sgro said the family were grateful for the Vatican's decision to open the tombs

The Vatican opened its own investigation into the case of Orlandi in April.

It followed the tip-off which advised the family's lawyer Laura Sgro to 'look where the angel is pointing'.

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

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

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 showed 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.

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

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

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

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

But she disappeared after a music lesson in Rome.

Her disappearance is one of the most enduring modern mysteries of the headquarters of the Catholic Church - and has been the subject of wild speculation by Italian media. Pictured: The angel-fronted tomb

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 the mystery.

Unproven theories on her disappearance include an attempt to secure the freedom of a gunman jailed for trying to assassinate Pope John Paul II, and a connection to the grave of Enrico De Pedis, a mobster buried in a Rome basilica. His tomb was opened in 2012 but nothing was revealed. Teutonic Cemetery is pictured from the dome of St Peter's Basilica

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

But DNA tests turned out negative.

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

For more than 35 years, Italian media have been obsessed with the fate of Emanuela, who would now be 51.