Tun Dr Mahathir Mohamad, in his fiercest attack on Malaysia's Prime Minister to date, said Datuk Seri Najib Razak had lost the trust of the people and that the Umno- led Barisan Nasional (BN) would lose the next general election with him at the helm.
Dr Mahathir also said Mr Najib had not adequately answered the allegations made against him.
"Malaysians... no longer trust Datuk Seri Najib. Umno members and their leaders must realise that Umno and with it BN will lose if Datuk Seri Najib leads Umno to GE14," he wrote on his blog.
"Once Umno loses, it cannot be rehabilitated any more," added Malaysia's longest-serving prime minister, who won five general elections before stepping down in 2003.
Dr Mahathir said it was difficult for him to write the strongly worded rebuke but that he did so out of loyalty to Umno. He also insisted his criticisms were not the ramblings of an old man.
"I have to expose all this. I am not senile although I am nearly reaching 90 years old."
In the blog post, he raised several issues that have dogged Mr Najib, including the 2006 murder of Mongolian interpreter Altantuya Shaariibuu and the debt-laden 1Malaysia Development Bhd (1MDB).
Dr Mahathir called for a new inquiry after one of the two men convicted of the murder - Mr Najib's former bodyguard Sirul Azhar Umar - claimed he had followed orders to kill her.
Ms Shaariibuu was at the centre of an alleged kickback scandal involving high-level Malaysian officials.
Mr Najib, who was defence minister at the time, has repeatedly denied any involvement in the case.
Dr Mahathir also expressed disappointment over Putrajaya's response regarding the troubled 1MDB and the involvement of businessman Low Taek Jho.
"There are many other allegations and questions against 1MDB that was set up by Datuk Seri Najib and which is controlled by him as adviser that have not been answered, other than to deny and call the allegations lies," he said.
Dr Mahathir also called Mr Najib's new private jet a waste of government money and questioned the source of funds for his stepson Riza Aziz's purchase of luxury properties in New York.
Supporting Dr Mahathir's call for answers was Umno veteran and his former political rival Tengku Razaleigh Hamzah.
"He wants to know the truth behind this. I am sure he must have his reasons for saying that," said the former finance minister, who came close to toppling Dr Mahathir as Umno president in 1987.
Although at least one Umno MP has called for the disagreements to be resolved in a "brotherly manner", party sources and analysts say they expect the attacks to intensify in the run-up to the Umno general assembly, which is expected to be held at the end of this year.
Observers say the man who would benefit should Mr Najib fall is Deputy Prime Minister Muhyiddin Yassin, though he has indicated before that he is not interested in the top post. They noted his absence from a recent gathering where Umno divisional chiefs pledged their loyalty to Mr Najib.
Political analyst Khoo Kay Peng pointed out that Dr Mahathir had backed Mr Najib until last year, when he withdrew his support, so it would reflect badly on him should Mr Najib fall.
"It is quite clear Dr Mahathir wants a change in leadership but this also reflects the weakness of his decision," said Mr Khoo.
Datuk Seri Abdullah Badawi succeeded Dr Mahathir as prime minister but was forced to step down in 2009 after disagreeing with the former leader on several key national policies.
Dr Azizuddin Sani, dean of International Studies at Universiti Utara Malaysia, said Dr Maha- thir's aim is to create momentum against Mr Najib within Umno and force a party election at Umno's annual general assembly.
Dr Shaharuddin Badaruddin, a research fellow at University Malaya Centre for Democracy and Election, said if Mr Muhyiddin does become the next premier, it would only be temporary.
"Dr Mahathir only trusts himself and the closest person to him is his son. (Kedah chief minister) Mukhriz is not in Parliament and you will need a transition prime minister and Muhyiddin is the best candidate."
This article was first published on April 3, 2015.
Get a copy of The Straits Times or go to straitstimes.com for more stories.