These investigations have cast an unflattering spotlight on the financial deal making, election spending and political patronage under Malaysian Prime Minister Najib Razak.

Here's a quick look at what the scandal is about:

1. WHAT IS 1MDB?

It's a government investment company that took shape in 2009 under Najib, who went on to lead its advisory board. Its early initiatives included buying privately owned power plants and planning a new financial district in Kuala Lumpur called Tun Razak Exchange (TRE).

But the fund proved better at borrowing than luring large-scale investment: it accumulated US$12 billion in debt.

2. WHAT'S THE ISSUE?

Investigators have been trying to trace whether money might have flowed through and around 1MDB and illegally into personal accounts. Some of the money is alleged to have ended up with Najib, his family and his confidant. That includes US$681 million from companies linked to 1MDB that landed in the prime minister's personal bank account, according to Wall Street Journal (WSJ).

Another $700 million in 1MDB funds meant for a joint venture with a company known as PetroSaudi International was found to have landed in an unrelated offshore account.

3. WHO ELSE IS MENTIONED?

Riza Aziz: Najib's stepson allegedly used money from 1MDB to buy homes in London, New York and Los Angeles and Street starring actor Leonardo DiCaprio, according to the WSJ report. The production company he co-owns, Red Granite Pictures, has said it believes none of its funding is "irregular or illegitimate".

Jho Low: The financier, whose full name is Low Taek Jho, is a family friend of Mr Najib and a high-profile art collector who said he did consulting work for 1MDB's predecessor. The WSJ report claimed he had alerted Najib's bank that "681 American pies" would be arriving just days before the $681 million was transferred. Low has said he provided consulting to 1MDB that did not break any laws.

Goldman Sachs: The company made $593 million working on three bond sales that raised $6.5 billion for 1MDB in 2012 and 2013, dwarfing what banks typically make from government deals. It said last year that fees and commissions "reflected the underwriting risks" it had assumed. New York's bank regulator has asked the firm for a summary of its 1MDB work.

BSI Bank: The Swiss bank that worked with 1MDB lost its license to do business in Singapore for breaches of money laundering rules. The Monetary Authority of Singapore (MAS) condemned poor management oversight and gross misconduct by some bank staff as it effected the first such shutdown of a merchant bank in Singapore in 32 years. BSI said it will cooperate with authorities.

UBS Group: It flagged suspicious transactions linked to 1MDB to the MAS, prompting an investigation of the accounts involved, a person familiar with the matter said. The transactions were not immediately recognised by UBS as suspicious, said the source. At least $1.24 billion was transferred in 2014 from the account of a 1MDB subsidiary held at BSI in Lugano, Switzerland, to a UBS account in Singapore held by what appeared to be a unit of an Abu Dhabi firm, investigative blog Sarawak Report said on July 11. A UBS spokesman declined to comment on the transfer.

Tim Leissner: The South-east Asia Chairman of Goldman Sachs wrote an unauthorized reference letter for Low on the bank's letterhead. He resigned in February and has not been accused of wrongdoing.

4. WHAT IS THE MALAYSIAN GOVERNMENT'S RESPONSE?

Najib, who is also Finance Minister, has always denied any wrongdoing and maintained that if any wrongdoing is proven, the law will be enforced without exception.

In January 2016, Attorney-General Apandi Ali cleared the prime minister of wrongdoing, saying the $681 million deposited into his personal bank account was a donation from the Saudi royal family, much of which was returned.

He said the Malaysian Anti-Corruption Commission (MACC) had recorded statements from witnesses, including the donor, and concluded that the money - deposited just prior to the 2013 General Election - was not "given corruptly" and was not used as "inducement or reward" for Najib to do anything in his capacity as Prime Minister.

He also said Najib returned $620 million to the Saudi royals in August 2013. But he did not say what the latter did with the remaining $61 million.

The Attorney-General had also rejected central bank requests for a criminal probe.

The Public Accounts Committee, a bipartisan parliamentary panel, also absolved Najib and blamed the financial and reporting lapses on 1MDB's former CEO Shahrol Halmi, who said he did nothing wrong. 1MDB officials also denied wrongdoing.

5. WHO ELSE IS INVESTIGATING?

There are probes related to 1MDB in several countries including Singapore, Hong Kong, Thailand, Australia, Britain, Switzerland and the United States. The investigations focus on possible embezzlement or money laundering.

The US Justice Department on Wednesday moved to seize more than $1 billion in assets, including luxury real estate and a jet, allegedly bought with money pilfered from 1MDB. Court filings made thinly veiled references to Najib, as the US alleged that billions of dollars were siphoned off by Najib's stepson, a family friend and other officials.

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