So much money was pouring so rapidly into the Malaysian Prime Minister's personal bank accounts that it rang internal money-laundering alarms inside AmBank, a major Malaysian institution part-owned by Australia's ANZ.

Key points: PM's personal account held under codename 'Mr X'

PM's personal account held under codename 'Mr X' Account received more than $US1 billion in two years

Account received more than $US1 billion in two years Millions of dollars spent on luxury hotels, cars and jewellery

Hundreds of millions of dollars were being wired into Najib Razak's accounts from the Saudi Arabian Government, a mysterious Saudi prince and two shadowy British Virgin Island companies, while the head of a Malaysian state-owned company topped up the Prime Minister's credit card accounts with millions of Malaysian ringgit in cash.

Mr Najib's Platinum Mastercard and Platinum Visa had been overdrawn thanks to a 3,320,670.65 ringgit ($US1,039,369.91) purchase of jewellery in September 2014 — a spending spree described inside AmBank as a "huge volume".

Mr Najib's wife Rosmah Mansor has previously been reported to have purchased a series of luxury items, from diamond jewellery to designer handbags, which appear beyond her husband's $A130,000 official annual salary.

Between opening his account at AmBank on January 13, 2011 and April 10, 2013, Mr Najib received a total of more than $US1 billion — or, more precisely, $US1,050,795,451.58 — including a series of individual deposits that ranged between $US9 million and $US70 million.

Inside the bank, the Malaysian Prime Minister's account was held under the codename "Mr X".

The startling new banking records have been obtained as part of a Four Corners program that aired last night, and which resulted in the arrest of two members of its team, Linton Besser and cameraman Louie Eroglu.

'Highly sensitive' report flags PM's unexplained wealth

The records also show that as well as spending some of the money on hotel accommodation and luxury cars, Mr Najib used the money to fund political affiliates in the run-up to Malaysia's last 2013 elections.

Four Corners has established that Dr Zeti Aziz, the governor of Bank Negara Malaysia, Malaysia's central bank, was repeatedly warned about the Prime Minister's unexplained wealth by senior officials at AmBank.

Sorry, this video has expired Four Corners reporter speaks of his arrest in Malaysia

At one such meeting in September 2012, the ABC has been told Dr Aziz handed back the bank's report, which had been marked "highly sensitive", not wishing for Bank Negara to have a copy on its premises.

When the ABC asked Dr Aziz what action she took when she received these warnings, she said there were limitations on the scope of investigations that Bank Negara could itself conduct, but that it always reported information it received to relevant authorities.

In January, the Malaysian Attorney-General shuttered a corruption probe of the Prime Minister, declaring Mr Najib had no case to answer.

Despite this, Dr Aziz said there remained ongoing investigations.

Asked who was behind the money flowing into Mr Najib's accounts, Dr Aziz said: "I cannot comment on this, it is an ongoing investigation."

Do you know more about this story? Email besser.linton@abc.net.au

'Absolute discretion' over use of 'Gift'

The remittances between 2011 and 2014 seen by Four Corners include payments by the Ministry of Finance in Saudi Arabia of $US49,999,988 on August 19, 2011, and $US29,999,988 on November 29, 2011.

There are also deposits recorded by AmBank as having come from a man named Prince Faisal bin Turkey bin Bandar Alsaud, of Riyadh.

These began on February 24, 2011, and continued into 2012 with $US49,999,965 deposited into Mr Najib's account on April 25, 2012, and another $US24,999,965 deposited on May 23, 2012.

These deposits were sometimes accompanied by letters to Mr Najib from a man described in the letter as "HRH Prince Saud Abdulaziz Al-Saud" which pledged gifts to the Malaysian Prime Minister which ranged from $US100 million on February 1, 2011, to $US800 million on March 1, 2013.

On November 2, 2011, for example, the letter pledged a grant of $US375 million, saying:

"This is merely a token gesture on my part but it is my way of contributing to the development of Islam to the world. "You shall have absolute discretion to determine how the Gift shall be utilised. "This letter is issued as a gesture of good faith and for clarification, I do not expect to receive any personal benefit whether directly or indirectly as a result of the Gift. The Gift should not in any event be construed as an act of corruption since this is against the practice of Islam and I personally do not encourage such practices in any manner whatsoever."

Multi-million-dollar 'donation' returned

There was another major source of funds to Mr Najib that has troubled investigators — a British Virgin Islands-incorporated entity called Blackstone Asia Real Estate Partners Ltd, which channelled its deposits via Standard Chartered Bank in Singapore.

The ultimate owner of the company has not been established, but it has been reported the company is associated with Low Taek Jho, known as Jho Low, a playboy financier at the centre of a highly controversial 2009 deal involving Malaysia's sovereign wealth fund, 1MDB.

Blackstone Asia Real Estate Partners paid Mr Najib $US69,999,988 on January 3, 2012, $US24,999,998 on March 13, 2012 and another $US24,999,988 on May 23, 2012.

Attempts to contact Mr Low were unsuccessful, but he has denied wrongdoing over the 1MDB deal.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 5 seconds 1 m 5 s Reporter Linton Besser questions Malaysian PM Najib Razak

It had previously been revealed by online news site Sarawak Report and the Wall Street Journal that a mystery BVI company called Tanore Finance deposited a total of $US680 million into Mr Najib's accounts in March 2013.

Two months ago Malaysian Attorney-General Mohamed Apandi Ali said $US620 million of this money was a "donation" that had subsequently been returned.

Now the new banking records show Mr Najib also received 4.3 million ringgit in cash top-ups that set off money-laundering alarms inside AmBank.

These were deposited by Nik Faisal Bin Ariff Kamil, the former investment director of 1MDB and chief executive of state-owned company SRC International. The files show he was a signatory to the Prime Minister's account.

In January 2014 he wrote an apologetic letter to an AmBank manager to explain why he had to so hurriedly deposit large volumes of cash into the account, explaining that "there will be occasions when I won't be able to provide necessary transfer authorisations to the account".

Large sums spent on holidays, cars

SRC International has been in the spotlight since it emerged it made a 27 million ringgit payment that also ended up in the personal accounts of Mr Najib.

That payment formed the basis for a criminal charge that was going to be laid against Mr Najib midway through last year, but which was aborted after the Attorney-General was suddenly removed from office.

The bank records also detail how Mr Najib used his new-found wealth. Much of it went to political affiliates in the lead up to Malaysia's last election in May 2013, including party officials, the Liberal Democratic Party and the Sarawak United People's Party, as well as various advertising and media firms.

A company called Solar Shine Sdn Bhd received the largest distribution — 24 million ringgit or $US3.5 million today.

Sorry, this video has expired Four Corners in Malaysia: 'No more questions please'

The company has been associated with an entity called 1Malaysia NGO which has run grassroots political campaigns on behalf of Barisan Nasional, the Prime Minister's party.

A sum of 7.5 million ringgit or $US1.9 million went to the Rahah Foundation, which hit the headlines in Malaysia when it donated cows alongside Mr Najib to the Selangor police to be sacrificed for Eid al-Adha, a Muslim ritual feast celebrated each year.

But there are other payments too that may not have had a political purpose.

These include 360,000 ringgit spent with fashion house Jakel Trading, 395,782.40 ringgit at the Shangri-la Hotel Kuala Lumpur, 178,000 ringgit spent with a company called Two One Holidays Malaysia and another 167,959.50 ringgit with Signature Exotic Cars, a dealer that specialises in Audi, Mercedes Benz and Porsche.

The files show Mr Najib directed cheques also to prominent businesspeople, academics and lawyers.

The Malaysian Prime Minister did not respond to written questions from Four Corners.

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