Voters turned out en masse to oust Najib, angered at rising living costs, divisive racial politics in the Muslim-majority country and allegations of endemic graft among the country's ruling elite.
Najib became a hugely unpopular figure over his alleged involvement in plundering huge sums from Malaysian sovereign fund 1MDB in a sophisticated fraud that is now being investigated in several countries.
Najib denies any wrongdoing in connection with losses at the fund.
The US Department of Justice has filed civil lawsuits alleging that over US$4.5 billion was misappropriated from 1MDB by high-level officials and their associates.
A total of US$681 million also mysteriously appeared in Najib's personal bank accounts in 2013 just ahead of a hotly-contested election. Najib has said the deposit was a donation by an unnamed member of the Saudi royal family which had been largely returned.
Mahathir, who earlier slammed Apandi's credibility, said the solicitor general will take over Apandi's job while he goes on leave.
"There have been a lot of complaints against the AG but no formal reports (lodged against him)".
"We are investigating various officers who the public have accused of wrongdoing, and if necessary, we have to stop them from leaving the country", said Mahathir at a press conference, without revealing the names.
Mahathir, at that time said he had to remove Anwar because he was "not fit for office".
According to the WSJ report, during the election campaign, Dr Mahathir vowed to free Anwar and pass the premiership to him, but said he would stay in the prime minister's post for two or three years to steer Malaysia in the right direction. He has ordered a travel ban on Najib and his wife and replaced the former attorney general Mohamed Apandi Ali, who was appointed by Najib.
Fernandes's apology did not seem to placate investors, as according to Reuters, shares in AirAsia tumbled almost 10 percent on Monday before closing down 5.4% in the first trading session after markets opened for the first time since the election.
Stocks initially lost 2.7% but quickly won back ground and closed 0.2% higher.
The ringgit currency hit a four-month low of 3.9850 per dollar, but stabilized off those lows.
But it has not been all smooth sailing since the historic win, with concerns over the slow formation of the cabinet as different parties in the winning alliance jostle for positions.
Meanwhile, Anwar's wife Wan Azizah Wan Ismail sought to dispel suggestions her husband wanted immediate power in the first place.
"The pardons board in Malaysia's capital will meet on Wednesday to discuss Anwar's release and Mahathir said he would be released the same day".
Anwar is serving a five-year jail term, his third stint in prison, for charges of sodomy he says were trumped up by the ousted premier Najib Razak. He has agreed to hand over power to jailed reformist leader Anwar Ibrahim but has not previously given any timing.
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.
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