JAKARTA (Reuters) - The speaker of Indonesia’s parliament, who is being investigated for his suspected involvement in a $170 million graft scandal, has tendered his resignation, two members of the assembly said on Monday.

Setya Novanto was arrested last month over his suspected role in the scandal linked to a national electronic identity card scheme.

Anti-corruption investigators then took him into custody from where he sent a letter to assembly leaders pleading to be allowed to keep his job while he fought the charges.

“Mr Novanto has resigned,” member of parliament Yandri Susanto told Reuters, referring to a letter in which Novanto announced his decision.

“He didn’t say why.”

A replacement for him as speaker was expected to be decided by his party, Golkar, at an extraordinary meeting on Dec. 19, said Dito Ganinduto, a member of parliament from Novanto’s Golkar party.

Novanto had not resigned as chairman of Golkar, Ganinduto said.

A lawyer for Novanto, Maqdir Ismail, deferred questions on the matter to acting Golkar chairman Idrus Marham.

Marham could not be reached for comment.

Novanto had clung to power through several previous corruption cases.

His latest battle with the graft agency has gripped Indonesia, where newspapers have splashed the story on front pages and social media posts mocking him have been widely shared.

Before his detention last month he had for months declined to answer summonses for questioning by the Corruption Eradication Commission, known by its Indonesian initials KPK.

The allegations against Novanto have reinforced the perception among Indonesians that their parliament, long regarded as riddled with entrenched corruption, is a failing institution.

Indonesia was ranked last year at 90 out of 176 countries on Transparency International’s corruption perception index.

The watchdog has singled out parliament as Indonesia’s most corrupt institution, and in July called on President Joko Widodo to protect the KPK against attempts by the legislature to weaken the commission’s powers.

Critics inside and outside the parliament say the root problem is money politics.