Newly elected Prime Minister Mahathir Mohamad, who was sworn in on Thursday, has vowed to investigate the 1MDB scandal and Najib.
Malaysia's attorney general rejected a recommendation in 2015 to investigate potential wrongdoing by then Prime Minister Najib Razak. "There will be no special powers given except as are given to ministers or deputy ministers or deputy prime ministers", he said. Swiss Attorney General Michael Lauber has been publicly critical of the lack of cooperation his team of prosecutors got from the government of former Malaysia premier Najib Razak, who himself has been accused of pocketing some of the diverted money.
Mahathir was spurred out of retirement by a corruption scandal at 1MDB, a state fund that is being investigated by the USA and several other countries after associates of defeated Prime Minister Najib Razak allegedly stole and laundered $4.5 billion from it.
"We think that within a short while we will have a case against him", Mahathir said.
Najib's popularity dropped sharply over the past three years, partly due to a scandal over 1Malaysia Development Berhad (1MDB), a state fund from which billions of dollars were allegedly siphoned off.
The report found, among others things, that 1MDB used 288 million ringgit ($73 million) of government funds to pay interest on its debt, which isn't in line with the fund's original goal.
Following his removal from power, Najib announced his resignation as president of the United Malay National Organisation (UMNO) party and the once-ruling Barisan Nasional alliance.
Mahathir, during his news conference at the administrative capital Putrajaya, said the government made a decision to bar certain individuals from leaving the country because their assistance was needed for the 1MDB probe.
Mahathir and Anwar (a jailed reformist) won the general election last week.
Najib set up 1MDB in 2009 and previously served as chairman of its advisory board. "There is no blacklist, we are only investigating various officers against whom we have gotten reports of wrongdoings", he said.
Arul Kanda, chief executive officer of 1MDB, and Najib's former aide, Abdul Razak Baginda, were also barred from traveling overseas, according to the sources who requested anonymity and said they were not authorized to speak to the media. U.S. investigators say some US3.5 billion was misappropriated from the fund. Mahathir hasn't said since the election if he will proceed with the plan.
Over the weekend, Mahathir barred Najib and his wife from leaving the country.
If found guilty, Najib faces up to 20 years in prison and a fine, legal experts said.
Mahathir also faced criticism for saying that a controversial law passed before the election that punishes "fake news" with up to six years in jail would be reviewed rather than revoked.
"I have given my assurance, I am here as a concerned citizen to give complete support to manage the country on the understanding that we are committed to the reform agenda, beginning with the judiciary, media and the entire apparatus", Anwar said in a news conference at his home after he was freed from custody. Singapore has punished banks over lapses related to 1MDB, seized assets and jailed bankers over the scandal.