A day earlier police said that Netanyahu's former spokesman tried to bribe a judge to drop a fraud case against Netanyahu's wife. Former Prime Minister Ehud Olmert went to jail for bribery in 2016 after his longtime secretary turned against him.
In the wake of the corruption accusations surrounding Benyamin Netanyahu, several Israelis were arrested in what the police are calling "Case 4000". Filber's change of heart could leave the tough-talking Netanyahu at his most vulnerable yet, with one critic writing him off as a "political corpse".
He has denied wrongdoing in what are now four separate investigations, including two in which he is personally a suspect.
The shekel, which had been strengthening recently, was down 0.1 percent at 10:40 a.m. Wednesday in Tel Aviv.
Mr Netanyahu is alleged to have pressed regulators so as to help the Bezeq telecoms giant in return for favourable news coverage from one of its websites.
Israeli Prime Minister Benjamin Netanyahu and his wife Sara attend an inauguration ceremony for a fortified emergency room at the Barzilai Medical Center in Ashkelon, southern Israel, February 20, 2018.
Fiber is seen as one of the architects of Netanyahu's 2015 election victory, after which he was appointed to head the communications ministry. "All decisions are transparent and controlled".
Netanyahu, 68, has disputed all the allegations. The defection of an aide as close as Filber turns up the heat. "It's not enough to just put the circumstances on the table".More news: Chelsea boss Conte: We need ideal game against Barcelona
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"The Netanyahu government's days are numbered, and we already need to prepare for the upcoming election in order not to be caught unprepared, because we are dealing with our internal election", Gilon said.
Another former Netanyahu confidant, Ari Harow, signed a similar agreement a year ago to cooperate with the police in other cases against Netanyahu.
Opposition politicians pounced on the news of Filber's defection. Mr Gabbay tweeted that the latest events had made it clear that the Netanyahu era was over.
The prime minister denies all the allegations against him and has said he will seek a fifth term in office in a national ballot due in late 2019.
Netanyahu posted an opinion poll commissioned by Likud on Facebook on Wednesday that showed that his party would boost its representation in the 120-member parliament from 30 seats to 34 if elections were held now. Netanyahu's personal attorney, who is also his cousin, represented the German firm involved and is suspected of using his influence over the prime minister in return for a hefty cut of the deal. "But I do hear some voices paving the way to defect the coalition when the time comes". "They are creating new cases every two hours".
In the second case, Netanyahu is accused of offering a newspaper publisher legislation that would weaken his paper's main rival in return for more favorable coverage.
The attorney general must now decide how to move forward with the police recommendations, a process that could take months. 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.
Two other suspected corruption cases have edged close to the prime minister without yet entangling him as a suspect. Its focus is an enormous deal for the purchase of naval vessels and submarines from the company.