The arrest took place a day after a senior police officer disclosed his involvement in another case of kidnap-murder of four persons, an issue which has snowballed into a major political challenge for Chief Minister Nitish Kumar.
Anant Singh was arrested in a 2014 case of kidnapping of a builder at Bihta in rural Patna, Senior Superintendent of Police Vikash Vaibhav said.
The Mokamah MLA, known for his strong arm tactics, has been kept in Sachivalay police station where a large number of his supporters gathered raising slogans.
The SSP said that six magazines of Insas rifle were found during the search at his official residence besides clothes soaked in blood, which would be sent for DNA test.
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While being taken away by the police, the MLA told reporters that he had not committed any wrong.
Though Singh was arrested today in an old case, the disclosure by outgoing SSP of Patna Jitendra Rana of Singh's alleged involvement in the June 17 case of kidnapping of four persons in his native Ladwa in Barh block of Patna district posed a challenge to Nitish Kumar government as RJD, ally of JD-U, demanded Singh's arrest.
Prasad had said the matter was an "acid test" for the new Patna SSP Vikash Vaibhav who had a tenure with NIA before coming to the state.