Rai arrived at the Bhagwanpur police station to give himself up from where the police arrested him, Hajipur police sources said.
"We have arrested Bachha Rai," Patna Senior Superintendent of Police Manu Maharaj, who is heading the Special Investigation Team (SIT) on merit muddle in Bihar's +2 examination, said.
"We will interrogate him intensively," Maharaj said.
Rai, a known supporter of RJD, had been allegedly eluding from police in the case.
Police will produce him before a local court by evening.
A police complaint had been registered against four students -- Sourabh Shrestha, Rahul Kumar, Ruby Rai and Shalini -- and Bachcha Rai in connection with Bihar School Examination Board merit muddle.
Another key accused, former BSEB chairman Lalkeshwar Prasad Singh is still absconding.
Following the furore over the Bihar Board examination toppers being unable to answer basic questions related to their stream eventually leading to a re-examination, Chief Minister Nitish Kumar had last week said that the guilty won't be spared, adding the investigation into this matter will be done with a criminal angle.
The Bihar Police SIT had on Thursday arrested five persons in connection with the state board exams scam.
The BSEB has since cancelled the results of two toppers, including Sourabh Shrestha, of the Intermediate (Science) exams after they failed to prove their merits in a re-test.
The board had on June 3 asked Sourabh and his college mate Rahul Kumar, who were among the 13 toppers from the arts and science streams in the Class XII examinations, to reappear in a re-test following a controversy over their merits.
Saurabh from the Science stream, who had secured 485 out of 500, was caught on camera failing to answer basic questions.
Ruby Rai, the arts topper, from the same college failed to take the re-test on Friday citing health reasons. Rai had secured 444 marks out of 500 in the Arts stream. However, on camera she did not even appear to know the number of subjects in her course.
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