A former aide of India's top opposition leader LK Advani, Sudheendra Kulkarni, has been arrested in connection with an alleged cash-for-votes scandal.
He is the sixth person to be arrested in the case. He denies any wrongdoing.
The most high-profile arrest so far has been of MP Amar Singh who is charged with offering cash to other MPs to abstain from a 2008 confidence vote.
Mr Kulkarni is alleged to have "master-minded" the operation. He says it was to expose corruption in the government.
Mr Kulkarni was an aide to senior Bharatiya Janata Party (BJP) leader LK Advani at the time of the vote.
He told the court on Tuesday that he was "a whistleblower" who intended to expose corruption.
Police allege that Mr Kulkarni approached Mr Singh's Samajwadi Party - an ally of the Congress-led government at the time of the vote - to offer bribe to BJP MPs.
He then got a television channel to secretly film the alleged bribe giving in order to nail the government, police allege.
BJP members waved wads of money in the air in parliament at the time of the debate, alleging that they had been offered bribes to abstain.
Amar Singh - a member of the Rajya Sabha, the upper house of the Indian parliament - was arrested on 6 September along with two former BJP MPs.
Faggan Singh Kulaste and Mahavir Bhagora were BJP lawmakers at the time of the vote. They are accused of accepting the bribe money. Both men have denied the charge.
The government survived the July 2008 vote. If it had been lost, India would have faced early elections.
The scandal resurfaced in March when a leaked US diplomatic cable obtained by the Wikileaks website said the Congress party had bribed MPs to vote in favour of the nuclear deal.
The cable alleged that the MPs had been paid $2.5m (£1.5m) each to buy their support.
In July this year, Supreme Court criticised the Delhi police for carrying out a "shoddy probe" into the scandal.