He has not been named a suspect in Case 4000.
One of Prime Minister Benjamin Netanyahu's closest and longest-serving aides appeared ready to incriminate him on Wednesday after agreeing overnight to become a government witness, the latest twist in a spiraling graft scandal that seemed to dim Netanyahu's legal and political chances of survival nearly by the hour.
Shaul Elovitch, a family friend of Prime Minister Benjamin Netanyahu who controls Bezeq through his Eurocom holding group, was arrested on Sunday along with his wife and son.
Police have not confirmed that Filber has turned state's witness, but Netanyahu quickly denied any wrongdoing and described the allegations as a witch hunt, madness and lies.
Israeli media allege, without confirmation from the police, that Filber has reached a deal with Israeli police to testify against Netanyahu in the case.
Israeli media reported that investigators were looking into allegations that Bezeq had received benefits in return for its owners offering favourable media coverage of Netanyahu on media they controlled.
Other leading Israeli columnists on Wednesday suggested that if Filber told all he knew, Netanyahu was probably more anxious about avoiding prison than staying in office.
Filber, the former director of the Communications Ministry under Netanyahu, is under arrest on suspicion of promoting regulation worth hundreds of millions of dollars to Israel's Bezeq telecom company. In return, police say Netanyahu operated on Milchan's behalf on US visa matters, legislated a tax break and connected him with an Indian businessman.
Israeli Prime Minister Benjamin Netanyahu was communications minister during the period when the illegal transactions allegedly took place.
"If Shlomo (Momo) Filber indeed signed a state's witness agreement last night, it is the end of an era", Ben Caspit wrote in the Maariv newspaper on Wednesday, calling him Netanyahu's "closest and most intimate covert operations officer".
Mr Filber, the prime minister's former chief of staff, election campaign manager and now director-general of...
Any actual indictment may be months away, pending a hearing with Netanyahu's lawyers and a decision by the attorney general.
The cases Netanyahu's aid allegedly sought to have dismissed involved his wife's alleged misuse of state funds for household and personal expenses.
Last week police said there were grounds to indict the prime minister himself, in two separate cases, for bribery, fraud and breach of public trust.
Netanyahu swiftly and angrily denied any suggestion that he made an offer to a potential attorney general as "ludicrous".