UPDATE 1-Milan prosecutors conclude AEM probe-sources

(Adds statement from A2A)

MILAN, July 8 (Reuters) - Milan prosecutors concluded an investigation into possible fraud to inflate gas bills, judicial sources said on Tuesday, a step in a process which could lead to the trial of nine people, including utility A2A's (A2.MI) chairman.

Prosecutors say Giuliano Zuccoli, who at the time was chief executive of AEM Milano, knew about an issue with meters which charged consumers for more gas than they had really used and tried to cover it up, the sources added.

A2A said in a statement it had nothing to do with any suggestion of fraud to consumers.

It added: "The anomalies on which the accusations are based ... are traceable to a temporary slowdown of billing in December 2004, because of changes made to modernize internal information systems."

It said this meant "the billing amount in 2005 was higher than the amount of gas sold during the year."

AEM Milano merged with ASM Brescia to form A2A at the start of this year. The investigation -- which has also looked at other companies in the utility sector, including Eni (ENI.MI) and Snam Rete Gas (SRG.MI) -- has been running for over a year.

Once prosecutors have concluded their investigation, a judge would have to decide whether to send the case to court.

Telephone intercepts showed that Alberto Solci, legal affairs manager for AEM and one of those under investigation, explained to colleagues how the meters malfunctioned, investigation documents showed, according to the sources.

His confident attitude "makes it evident that Zuccoli was fully informed of the situation," the investigation documents said, according to the sources.

Another conversation between Zuccoli and his secretary showed that he "not only worked ... to give instructions on obstructing any possible legal processes but also took other measures to cover up the past," the documents said.

The other AEM personnel under investigation are Patrizia Savi and her colleague Daniela Martinazzi, Dario Cassinelli, Aldo Scarselli, Roberto Gilardi and Luigi Guarrera. (Writing by Jo Winterbottom; Editing by Paul Bolding and Gerald E. McCormick)