Malaysian prosecutors have not appealed former Prime Minister Najib Razak’s acquittal in a case of audit tampering involving state fund 1MDB, his lawyers said on Tuesday, risking blowback for Prime Minister Anwar Ibrahim, who has vowed to combat graft.

Anwar is already under pressure from supporters and the opposition after his government dropped dozens of bribery allegations last week against a key ally whose support is critical for the premier to maintain his parliamentary majority.

Najib, 70, is serving a 12-year jail sentence for another corruption case linked to 1Malaysia Development Berhad (1MDB). He also faces several other graft charges.

The attorney-general’s chambers was expected to appeal Najib’s acquittal earlier this year of a charge of abusing his position as prime minister to amend a government audit into 1MDB .

But Najib’s lawyers at Shafee & Co said in a statement, “the prosecution evidently found no grounds for appeal” and did not file the petition.

Najib had pleaded not guilty.

An estimated $4.5 billion was allegedly misappropriated from 1MDB by high-level officials of the fund and their associates between 2009 and 2014, the U.S. Justice Department has alleged.

Anwar, who came to power in November last year, had vowed to fight corruption as part of his election campaign. But concerns were raised after he partnered with Najib’s corruption-tainted party to form a government and appointed officials accused of graft to senior positions.

On Sunday, the Malaysian United Democratic Alliance said it was leaving Anwar’s ruling coalition, citing concerns after graft charges were dropped against Ahmad Zahid Hamidi, the country’s deputy premier.

Anwar has maintained that the move to drop the case, which triggered a widespread public backlash, was made without his interference.