MANILA - A former senator embroiled in one of the largest corruption scandals to hit the Philippines was acquitted of plunder on Friday (Dec 7).

An anti-graft court ruled that prosecutors had failed to prove that Ramon Revilla Jr, 52, a popular actor and an ally of President Rodrigo Duterte, had a hand in the misuse of 224.5 million pesos (S$5.8 million) worth of "pork barrel" funds that went through his office.

A pork barrel refers to government funds for projects by lawmakers meant to please voters and win votes.

But Revilla's aide, lawyer Richard Cambe, and political fixer Janet Napoles, the purported mastermind behind the scam, were found guilty of plunder. They were each sentenced to up to 40 years in jail.

Napoles, 54, allegedly set up "dummy" foundations that she used to channel at least 10 billion pesos (S$260 million) worth of funds meant for non-government and charity organisations into the private accounts of politicians she dealt with as a consultant and contractor.

Napoles turned herself over to then President Benigno Aquino in April 2013, after she briefly went into hiding.

She later named Revilla and two other senators at the time - Juan Ponce Enrile and Jinggoy Estrada - as among those who supposedly received "kickbacks" from her.

The three senators were arrested in 2014 in what was then hailed as the high point of Mr Aquino's anti-graft push.

Enrile, 94, was defence minister under the regime of the late strongman Ferdinand Marcos.

Estrada, 55, is the son of former president Joseph Estrada.

Both Enrile and Estrada were allowed earlier to post bail.

In his campaign speeches, Mr Duterte had vowed to have Estrada and Revilla released from detention. He claimed the two had been targeted by Mr Aquino for political persecution.

when asked if he expected the ruling, Revilla told reporters: "Of course, because I know that I'm not guilty. I had been saying that all along."

Under intense grilling from Revilla's lawyers during the trial, witnesses presented by prosecutors recanted statements they had issued implicating Revilla.

One whistle-blower, Ms Marlina Sula, who worked as a clerk for Napoles, said she never met or witnessed Revilla receiving money from Napoles.

She testified that she instead saw a fellow whistle-blower, Mr Benhur Luy, who worked as records keeper for Napoles, forge Revilla's signatures in letters endorsing Napoles' bogus organisations.

Prosecutors, she added, had coerced her into backing Mr Luy's testimonies.

Revilla still faces 16 counts of graft. He posted 480,000 pesos in bail, so he could be set free after four years of detention.

He is currently running for senator.

A regional trial court sentenced Napoles to 40 years in prison in 2015 for detaining Mr Luy just before the scandal broke following stories published by the Philippine Daily Inquirer.

An appeals court reversed Napoles' conviction in May last year, saying it found the evidence against her "grossly insufficient to sustain a conviction".

Napoles, however, was kept in jail for other charges filed against her.

Critics claim Napoles is now being cajoled into turning state witness against Mr Aquino, whom Mr Duterte has linked to efforts to destabilise his government.

Mr Aquino is facing accusations that he circumvented the law in bypassing Congress to fund his infrastructure projects.