The head of Indonesia's powerful anti-corruption watchdog has been arrested on suspicion of murder amid claims of a love triangle and a conspiracy to destroy the high-profile crime fighter.

Antasari Azhar, 56, arguably Indonesia's most powerful legal figure, has overseen a series of successful fraud investigations into government officials and institutions since taking over as head of the Corruption Eradication Commission (KPK), set up two years ago to combat Indonesia's culture of graft.

His arrest as a suspect in the murder of Nasrudin Zulkarnaen, a prominent businessman, is a blow to President Susilo Bambang Yudhoyono, whose image has been boosted by the crackdown on corruption and who is seeking re-election on a platform of good governance.

Mr Azhar's lawyer denied that his client masterminded the murder of Mr Zulkamen, the director of a major state-owned pharmacy, describing the killing as a "grand scenario" to destroy an honourable crime fighter.

Mr Azhar has not been charged with the crime, and has denied any involvement. He refused to comment as he was led away by police, but over the weekend he said that his efforts to put corrupt politicians, lawmakers, bankers and businessmen behind bars had earned him many enemies.

Mr Zulkarnaen, the director of PT Putra Rajawali Banjaran, was shot throught the window of his BMW by two gunmen on motorbikes as he was leaving a golf course on the outskirts of Jakarta, the capital, on March 14.

Two days after his murder, police reportedly found a text message on his mobile phone from Mr Azhar saying: "You know the risk."

Police were also alerted to Mr Zulkarnaen's involvement with a 22-year-old golf caddy with whom, Mr Zulkarnaen's family claim, Mr Azhar was also infatuated.

A friend of Mr Zulkarnaen claimed that the businessman threatened to expose Mr Azhar's relationship with the young woman, named by Indonesia media as Rani Julianti. Jeffrey Lumempouw, a golf partner of Mr Zulkarnaen, told Indonesian journalists that he was told of the text message on the course just hours before the murder.

However, colleagues pointed out that the businessman was also a witness in a graft case concerning his own company, raising the possibility that he may have been killed by corrupt colleagues who feared exposure, and who then set out to frame Mr Azhar.

Police have already arrested the alleged killer and his alleged recruiter – reported to be a senior police officer. The owner of the newspaper Harian Merdeka is accused of financing the plot and has been arrested along with one other alleged financier.

Mr Azhar said that he respected the legal process and would co-operate with authorities.

"I and my family are ready to face this case," he said.

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