The unsolved case of a 15-year-old girl who went missing in Rome 25 years ago has been dramatically reopened.

A woman has told police the girl was kidnapped by a criminal gang on the orders of Archbishop Paul Marcinkus, the disgraced former head of the Vatican's bank who was linked to the death of the Italian banker Roberto Calvi.

The disappearance in June 1983 of Emanuela Orlandi, the daughter of a Vatican employee, has previously been linked by criminal informants to the Rome-based Banda della Magliana gang. But new details supplied by Sabrina Minardi, former girlfriend to the gang's boss, Enrico De Pedis, now ties in the Holy See official.

Minardi has claimed De Pedis snatched the girl on the orders of Marcinkus "to send a message to someone above them" as part of a "power game", La Repubblica newspaper reported yesterday, quoting her testimony.

After being held then killed, Orlandi's body was put in a sack and hidden in a cement mixer on the outskirts of Rome, Minardi said.

American-born Marcinkus died in 2006 aged 84, taking to the grave the truth about his suspected links to the collapse of Italy's Banco Ambrosiano in 1982 and his association with Michele Sindona, a convicted fraudster linked to the mafia who died in prison in Italy in 1986 after drinking coffee laced with cyanide.

As head of the Vatican bank, Marcinkus oversaw the Holy See's stake in Banco Ambrosiano and knew the bank's chairman, Roberto Calvi, who was found hanged from Blackfriars bridge in 1982.

Marcinkus was protected by Vatican diplomatic immunity from questioning about his role in the bank's collapse although the Vatican paid out $250m to creditors.

Minardi has told investigators that De Pedis carried out Marcinkus's order to kidnap Orlandi in return for the archbishop's help in investing cash overseas from the proceeds of other kidnappings undertaken by the Rome gang. That cash was delivered to the archbishop's apartment in Louis Vuitton bags, Minardi said, adding that she knew the apartment because she would take girls there on Marcinkus's orders.

Members of Orlandi's family, who have plastered Rome this week with missing posters to commemorate the anniversary of Emanuela's disappearance, said they were sceptical of the claims made by Minardi, who has been treated for drug abuse. Investigators remained cautious but are impressed by the accuracy of some details, La Repubblica said.

Previously, the Banda della Magliana was reported to have kidnapped Orlandi to bargain for the release of Mehmet Ali Agca, the Turkish gunman who shot Pope John Paul II. According to that theory, Orlandi is alive and possibly living in Turkey.

Before her affair with De Pedis, Minardi had been married to Lazio footballer Bruno Giordano.

Despite his criminal credentials, De Pedis was buried in the church of Saint Apollinaris in Rome after he was shot dead in 1990.