Jerusalem (CNN) Charges of bribery, fraud and breach of trust have been unveiled against Prime Minister Benjamin Netanyahu in three separate corruption cases, the Attorney General announced on Thursday evening, marking the first time in Israel's history that a sitting PM faces indictment in criminal investigations.

During a final pre-indictment hearing last month, Netanyahu's high-powered legal team tried to convince prosecutors to close the cases, including the most serious charge of bribery. But Avichai Mandelblit , a Netanyahu appointee who once served as his cabinet secretary, is moving forward. "It is a very sad day for Israel and for me personally," said Mandelblit, adding that the decision to indict "is not a matter of politics, of right and left."

Speaking in Jerusalem on Thursday night, Netanyahu described the charges as "an attempted coup against a Prime Minister" and vowed to continue to lead the country.

Israel's deadlocked parliament means that a formal indictment may still be months away. Nevertheless, the charges are a significant blow to Israel's longest-serving Prime Minister , who has held office for a total of more than 13 years. He has proclaimed his innocence ever since the criminal investigations became public nearly three years ago.

As the investigations advanced, Netanyahu refused repeated calls from opposition lawmakers to step down. Unlike a government minister, or ordinary lawmaker, who must resign his position if indicted, a Prime Minister is under no such obligation. Instead, he or she is only required to step down after any conviction and subsequent appeals process has played out, which could take years.

Netanyahu and his allies have conducted a campaign to delegitimize the investigations since they were made public in January 2017. Characterizing the legal process as a media-fueled witch hunt, he has often promised, "There will be nothing because there is nothing." But as the probes advanced and Netanyahu faced more than 10 rounds of questioning, "nothing" turned into something quite significant.

Case 4000

Mandelblit laid out the foundation of the criminal charges in a 57-page filing in February, when he announced he would pursue charges of bribery and breach of trust.

In the most serious case, known as Case 4000, prosecutors say Netanyahu advanced regulatory benefits worth more than 1 billion shekels (approximately $280 million) to his friend, millionaire Shaul Elovitch, who owned the Walla! News website as part of his control of the Bezeq telecommunications company.

Prosecutors say that in exchange, Netanyahu, who also served at that time as Israel's Minister of Communications, received favorable news coverage on Walla! as well as influence over the choice of stories and language used.

Mandelblit described the relationship between Netanyahu and Elovitch as "intensive, frequent, and extraordinary," adding that relations involving the wives of the two men were at a similar level.

"Elovitch gave you the above-mentioned favors in the expectation and mutual understanding that with regard to your power, position, and authority, you ... would be able to help him promote matters that would give him, directly or indirectly, enormous benefits of a business and financial nature," Mandelblit wrote in his February filing.

Beginning in late 2012, prosecutors say Netanyahu made "hundreds of demands, sometimes on a daily basis" for more positive news coverage, especially during election periods. On election day in 2015, prosecutors say Netanyahu demanded that the website feature prominently a video in which he declared, "The Arabs [are] going to the polls in droves."

Netanyahu conveyed his demands to Elovitch directly, prosecutors say, as well as through some of those closest to him, including Shlomo Filber, then serving as Director General of the Ministry of Communications, and Nir Hefetz, who was the Netanyahu family spokesman at that time. Both Hefetz and Filber became state's witnesses during the investigation period, providing evidence and testimony against their former boss. Netanyahu's former chief-of-staff, Ari Harow, also became a state's witness.

In a series of extensive transcripts of conversations related to Walla! News coverage of Netanyahu, prosecutors laid out a pattern of behavior in which Netanyahu, either directly or through intermediaries, would demand that stories be published, headlines changed and coverage altered.

In 2015, Netanyahu appointed Filber -- then one of his closest confidants -- to the position of Director General in the Ministry of Communications and allegedly instructed him to fast-track approval of a merger between Bezeq and another telecommunications company called Yes.

The merger directly benefited Elovitch because of his stake in Bezeq. Prosecutors say Filber maintained a secret channel with Elovitch and other Bezeq officials to keep them updated on the approval status of the merger. At the same time, the Bezeq officials allegedly made their own demands regarding the wording of the merger approval, insisting the deal be approved with no major changes.

Netanyahu has insisted that all of the decisions regarding Bezeq and the merger with Yes were made only after consultations with legal professionals and industry experts. Elovitch, who faces potential charges of bribery, has also denied any wrongdoing.

In the other two cases against Netanyahu, known as Case 1000 and 2000, he faces two charges of fraud and breach of trust, one from each investigation. In Israel, fraud and breach of trust is a single charge.

Case 1000

In Case 1000, prosecutors say that between 2011 and 2016 Netanyahu received gifts from overseas businessmen, including expensive cigars and champagne, which later turned into a "supply line." The value of the gifts was approximately $200,000. In particular, the gifts came from Hollywood producer Arnon Milchan and Australian businessman James Packer.

"The deliveries of champagne were generally made at your wife's request," prosecutors wrote. "The deliveries of cigars were sometimes made at your request as well."

In return for the gifts, prosecutors say, Netanyahu helped Milchan with visa applications to the United States, even asking then-Secretary of State John Kerry to intercede to make sure the visa was approved. Netanyahu also allegedly sought to pass tax amendments that would have benefited Milchan, even as Israel's Finance Minister at the time expressed reservations about granting the exemption.

Milchan and Packer have both proclaimed their innocence. Netanyahu has also said he and his wife did nothing wrong and that the gifts were exchanges between friends.

Case 2000

In Case 2000, prosecutors say Netanyahu sought to make a deal with Arnon "Noni" Mozes, the owner of Israel's Yedioth Ahronoth newspaper, that would have seen Netanyahu receive more favorable coverage.

In return, the Israeli leader would then pursue legislation that would limit the circulation of Yedioth Ahronoth's rival, Israel HaYom; at least that is what Netanyahu wanted Mozes to believe, prosecutors say. The largest newspaper in the country, Israel HaYom, is owned by Sheldon Adelson and is widely seen as a mouthpiece for Netanyahu.

Netanyahu met with Mozes in three separate rounds of meetings between 2008 and 2014, as the two talked about the details of the arrangement, but no agreement was ever reached, according to prosecutors. Mozes proposed hiring writers who would work on Netanyahu's behalf while publishing negative articles about Netanyahu's rivals. Improving the coverage of Netanyahu was euphemistically called "turning the board around."

Addressing Netanyahu directly in the filing, prosecutors wrote, "(Y)ou... (were) clearly taking advantage of your public role, which was the reason that Mozes contacted you with an offer of a bribe, and you led him to believe that you would consider the possibility of using your governmental power to promote the legislation that would benefit him, even though you had no real intention of doing so."

Both Netanyahu and Mozes have said they were not serious discussions; rather, they each claim they were trying to expose the other's lack of trustworthiness. Mozes, who faces a potential charge of bribery, has insisted he is innocent.

The attorney general decided not to pursue charges of bribery in Case 1000 and Case 2000.

Netanyahu and allies attack judiciary

Netanyahu has argued that the investigations against him were unfair and that numerous details of the cases were leaked to the media. Responding to the charges on Thursday, he complained bitterly about what he portrayed as double standards, railing against the fact that dozens of lawmakers had not been investigated earlier for what he portrayed as similar allegations involving an Israeli newspaper.

"There is one law for others, one law for Netanyahu," he said.

Even before the charges were unveiled, his attacks on the judiciary, the police and state prosecutors were escalating. Late last month, Minister of Justice Amir Ohana, considered one of Netanyahu's closest party colleagues, accused prosecutors of running a "state attorney's office within the state attorney's office" which acts "according to the political order of the day."

"In this way, they became a player on the political field, a player that is not up for public election," Ohana said late last month.

The unprecedented attack on part of his own office prompted an unusual rebuke from both Mandelblit and State Prosecutor Shai Nitzan, who said they "deeply regret the words of the Justice Minister."

"We reject the attempts to show fault in the work of police and prosecution elements without any factual basis," the two wrote in a joint statement. "No one will deter us from carrying out our work faithfully. No one will divert us from the right path."

The Chief Justice of the Supreme Court of Israel, Esther Hayut, warned the continued attacks were a danger to the functioning of the country's democracy. "Politicization of the justice system could completely undermine its foundations as an independent system and damage the public trust in the judicial branch," she said in October.

What's next for Netanyahu

Netanyahu will now face growing calls from politicians and the public for him to resign. So far, he has refused any such demands.

Crucially, he remains the leader of Israel's right wing, retaining the support of his own Likud party, as well as of the religious Zionist and ultra-Orthodox parties. If his allies deem him more of a liability than an asset, they could seek to remove him, but so far there is no indication that such a move is imminent.

The indictment comes as Israel finds itself in an unprecedented political situation. On Wednesday, former IDF Chief of Staff Benny Gantz gave up on his attempts to form a government, four weeks after Netanyahu was forced to declare failure in his efforts to do the same.

Israel is now in a 21-day period where any member of Knesset who can muster the support of a majority of lawmakers can become Prime Minister. In theory that includes Netanyahu, but news of the Attorney General's final decision makes it less likely that any opposition lawmakers would cross over to give him their support.

"A Prime Minister up to his neck in corruption allegations has no public or moral mandate to make fateful decisions for the State of Israel," said Gantz's Blue and White party in a statement on Thursday. It is unclear at this stage whether Thursday's announcement means the Prime Minister might start to lose the support of his bloc to Gantz.

The political deadlock also means the legal process will move more slowly. As Prime Minister, Netanyahu is under no obligation to stand down if indicted, but the Speaker of Parliament is still required to ask him whether he intends to exercise his immunity.

Netanyahu's response to that question needs to be adjudicated by the Knesset House Committee, which is only due to be constituted once a new government has been formed. That could be many months away, although the process could be expedited if the Supreme Court is asked to rule on a request to move forward with a trial.