Malaysia's former prime minister Najib Razak
Malaysia's former prime minister Najib Razak leaves after giving a statement to the Malaysian Anti-Corruption Commission (MACC) in Putrajaya, MalaysiaREUTERS/Lai Seng Sin

Embattled former Malaysian prime minister Najib Razak has filed lawsuits against top investigators probing a multi-billion dollar scandal at state fund 1MDB, as he looks to clamp down on public criticism over his alleged role in the case.

Najib, who lost power in a shock election defeat in May, was arrested and charged in connection with suspicious transactions at SRC International, a former unit of the fund. Najib, who has consistently denied any wrongdoing regarding 1MDB and SRC, on Wednesday pleaded not guilty.

In a legal counterattack, Najib is suing three top officials involved in the investigation into the fund, 1Malaysia Development Berhad (1MDB).

In three civil filings made last week but only made available to Reuters on Wednesday, Najib's lawyers alleged that anti-graft chief Mohd Shukri Abdull, police commercial crimes head Amar Singh and Attorney General Tommy Thomas was prejudiced against him over the course of their investigations.

Badrul Abdullah, who leads one of two Malaysian legal firms representing Najib, said the applications were based on past statements made by the three individuals. Court records show the three applications were filed on June 30, and name Najib, who held power for about 10 years, as the applicant.

In May, Shukri said a 2015 investigation into 1MDB was suppressed, while Singh has led police seizures of nearly $275 million worth of luxury goods from premises linked to Najib's family.

Thomas is the lead prosecutor who on Wednesday charged Najib with three counts of criminal breach of trust and one for abuse of power, related to 42 million ringgit ($10.39 million) allegedly transferred into his account from SRC.

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Najib and his family have come under intense public scrutiny over the past two months since he lost the election to his former mentor-turned-foe, Mahathir Mohamad, who reopened domestic probes into 1MDB as one of his first acts as prime minister.

The 1MDB scandal has been raging since 2015, but only now is it being freely discussed by mainstream media in Malaysia, which was tightly controlled during Najib's premiership. The nation was gripped by regular live streams by local news portals, broadcasting developments of Najib's case from the time police raided his family's residences to his court appearance.

Mahathir and some of his cabinet have been outspoken about the case. Najib has said he is a victim of political vengeance.