The Malaysian Anti-Corruption Commission effectively cleared Najib of any criminal wrongdoing. In early July, The Wall Street Journal reported that the money came into Najib's accounts from entities linked to the 1MDB state investment fund.
The commission said in a statement that its investigation showed the money was "contributions from donors, and not funds from 1MDB"and that it had referred its findings to the attorney-general. It did not identify the donors or say how the money was spent.
Last month, then-Attorney General Abdul Gani Patail confirmed receiving documents from investigators that linked Najib to 1MDB fund. The documents could pave the way for possible criminal charges and have embroiled Najib in the biggest crisis of his political career.
The government last week abruptly terminated Gani's services, three months short of his retirement. Najib has also axed his deputy Muhyiddin Yassin, a vocal critic, and four other ministers in a surprise Cabinet reshuffle.
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"In my view, the statement by MACC still causes me concern as it means whoever donated such large sums is likely to expect benefit," said lawyer Ambiga Sreenevasan, who heads the National Human Rights Society.
Before the anti-graft statement, opposition lawmaker Rafizi Ramli earlier Tuesday predicted that Najib would claim that the money came from donations from rich individuals in the Middle East, which would halt investigations into the money in his account.