New Delhi, The CBI on Monday arrested Raj Kumar Singh, believed to be a key accused in the murder of West Bengal Chief Minister Suvendu Adhikari's aide Chandrakant Rath, officials said Monday.

Singh, who also goes by an alias of Raj Singh, was arrested from Muzaffarnagar in Uttar Pradesh by a team of CBI, they said.

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Rath, the personal assistant to Adhikari, was shot dead in Madhyamgram on May 6, two days after the declaration of the fiercely contested West Bengal Assembly poll results.

The CBI has taken over the probe into Rath's murder from the West Bengal Police following a request from the state government.

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The central agency has formed a seven-member special investigation team under a DIG of Special Crime from Delhi, comprising some of the best investigators drawn from its various units, the officials said.