VATICAN CITY (AP) — The mystery of the 1983 disappearance of the 15-year-old daughter of a Vatican employee took yet another twist Saturday following excavations this week at a Vatican City cemetery. The Vatican said it had discovered two sets of bones under a stone slab that will be formally opened next week.

The new discovery came after Vatican on Thursday pried open the tombs of two 19th-century German princesses in the cemetery of the Pontifical Teutonic College in hopes of finding the remains of Emanuela Orlandi.

Orlandi’s family had received a tip that she might be buried there. But the tombs turned out to be empty, creating yet another mystery about where the dead princesses were.

The Vatican vowed to keep investigating and noted that any bones in the tombs might have been displaced during structural work carried out on both the college building and a cemetery near St. Peter’s Basilica in the 1800s and in more recent decades.

On Saturday, Vatican spokesman Alessandro Gisotti said further searches had centered on the areas adjoining the princesses’ tombs. He said investigators had located two ossuaries, or sets of bones, under a stone slab manhole covering inside the Teutonic college itself.

He said the area was immediately sealed off and would be opened in the presence of forensic experts on July 20.

Gisotti added that the bones were found in two holes carved out of a large stone that was covered by an old pavement stone a few meters (yards) behind the princesses’ tombs. That area is now technically inside a building of the Teutonic College, after expansion work on the building encroached onto the cemetery field.

The last recorded structural work done on the building and the cemetery was in the 1960s and 1970s. Orlandi disappeared in 1983.

She vanished after leaving her family’s Vatican City apartment to go to a music lesson in Rome. Her father was a lay employee of the Holy See.

Her case has been one of the enduring mysteries of the Vatican, kept alive by the Italian media and a quest by her brother to find answers. Over the years, her disappearance has been linked to everything from the plot to kill St. John Paul II to the financial scandal of the Vatican bank and Rome’s criminal underworld.