By Emilio Parodi
MILAN (Reuters) - Three employees of companies owned by infrastructure group Atlantia <ATL.MI> were placed under house arrest on Friday, police said, as part of an investigation into the safety of motorway viaducts following a bridge collapse in Genoa.
The collapse of the Genoa viaduct, operated by Atlantia-controlled Autostrade per l'Italia, in August last year killed 43 people.
The tax police said in a statement on Friday they had found evidence that safety reports for some viaducts operated by Autostrade had been falsified, or information had been omitted, with the aim of misleading transport ministry inspectors and avoiding further checks.
Shares in Atlantia, which is controlled by the Benetton family, closed down 8.1% as a senior politician renewed calls for the company to be stripped of its motorway concession following the arrests.
The three people placed under house arrest are employed by Atlantia's motorway unit Autostrade per l'Italia and maintenance company SPEA Engineering, the police said, without giving more details.
Six other people at the same companies were temporarily banned from holding office, the police said, adding that the offices of the people targeted by the probe had been searched.
Atlantia said in a statement it would launch an immediate audit to determine whether internal procedures had been followed correctly by the companies and people involved in the probe.
It said the audit would be led by a leading international company, which it did not name, and its outcome would be made available to investigating magistrates.
It added it had requested the boards of the two units involved to meet urgently on the matter.
In a separate statement, Autostrade per l'Italia said all the viaducts targeted by the investigation were safe, adding it had already moved the officials under house arrest to different jobs.
A Milan trader said the arrests had revived concerns that the Italian government could make good on a threat of revoking the company's motorway concession, which accounts for one third of the infrastructure group's core profit.
A senator of Italy's 5-Star Movement, a party in the ruling coalition government, said Atlantia must lose the concession.
"Measures taken against some Autostrade per l'Italia's officials this morning are based on the hypothesis of false reports on the actual maintenance of other viaducts ... all this is unacceptable and must lead to a revocation of the concessions," said Agostino Santillo, who is also a member of the transport committee of Italy's Senate.
The 5-Star Movement has been the most vocal against Atlantia since the collapse of the bridge in Genoa, with the other party in a new governing coalition, the Democratic Party, more inclined towards reviewing the terms of the concession but not revoking it altogether.
Atlantia and the two units have been under scrutiny since the collapse of the Genoa viaduct. Around 70 employees at Atlantia and the transport ministry are already under investigation in a separate probe into the causes of the disaster.
Atlantia has always denied any wrongdoing.
(Additional reporting by Francesca Landini and Silvia Aloisi; Editing by Susan Fenton and David Evans)