Rakesh Pandey was arrested on Tuesday by CBI sleuths at the Ghazipur area of Uttar Pradesh and produced before a court, which remanded him to the agency's custody for 10 days, CBI sources said in New Delhi on Friday.
During investigations, the CBI claimed to have found that Pandey was among the group of people who fired at Rai on November 29, 2005 while he was on his way to his home, they said.
Sanjeev Maheshwari, against whom the CBI filed a supplementary chargesheet in the case on August 31, has also named Pandey, sources said. Pandey allegedly used an AK-47 rifle to shoot Rai.
The CBI has alleged Rai was murdered by Maheswari, Firdaus, Atta-ur-Rehman, Azaz, Munna Bajrangi and other associates of independent MLA Mukhtar Ansari and Samajwadi Party MP Afzal Ansari.
CBI said the hunt was on to nab Bajrangi and Rehman, who have been absconding since Rai was killed.
The CBI had registered a case against Bajrangi, Mukhthar Ansari, Afzal Ansari, Aizaz Ahmed, Atta-ur-Rahman and Firdaus under various sections of the Indian Penal Code and the Arms Act for allegedly conspiring and murdering Rai.
The case was handed over to the CBI by the Allahabad High Court on May 23 after Rai's wife Alka approached the court with a petition requesting the transfer of the probe to the agency as she was unhappy with the investigation by Uttar Pradesh Police.
