Human remains found at property in Rome owned by the Vatican belonged to an ancient Roman man and not to either of two teenage girls missing since the early 1980s, authorities have said.

The discovery of the remains in October raised hopes of a breakthrough in the cases of Mirella Gregori and Emanuela Orlandi, both of whom were 15 when they disappeared within weeks of each other in 1983.

Mirella was last seen on 7 May after telling her mother she had a date, and Emanuela on 22 June as she left for a music class.

Initial reports suggested tests on the remains showed they were those of a woman. There was speculation that they could be the remains of two people, after an almost complete skeleton was found in one area and bone fragments in another.

But investigators closed the case on Friday, saying the remains belonged to a man who died of natural causes between AD90 and AD230.

The discovery of the remains, made during restoration work of a floor of a building annexed to the Vatican’s embassy, had given the girls’ families hope of finally knowing what happened to the them.

The first report came from the Italian news agency Ansa, which cited a Vatican source as saying the remains could belong to Emanuela. “The source wasn’t invented,” Emanuela’s brother Pietro Orlandi told the Guardian. “He went to the site and said the remains could be Emanuela.”

Antonietta Gregori, Mirella’s sister, said: “We were hoping to bring an end to this dramatic story after 35 years.”

The families are now bewildered as to how experts were unable to immediately recognise that the remains were ancient. Orlandi said: “Straight away they said the remains were well maintained and recent. Now they say they are 2,000 years old.”

Laura Sgrò, the lawyer representing the Orlandi family, said: “We don’t understand how they could have made so many speculations, also because so many experts in the field say you can immediately identify extremely old remains by their colour. It’s crazy and has caused the family so much pain. Someone should take responsibility.”