GRP sources said Chhathu Sahni, a resident of Takiya at Bhagalpur, was picked up from the Khagaria railway premises yesterday.
The administration had earlier suspended Naugachia GRP station SHO Manish Kumar for alleged failure to cooperate in the investigation into the case relating to the killing of the researcher.
The police had found a rucksack belonging to Pritam.
The rucksack was found nearly 300 metres away from the place near Kataria Railway Station where the body of Bhattacherjee had been dumped by his killers, GRP sources said.
Pritam had gone missing from Naugachia Railway Station on July 9 and his body was recovered on July 15.
Inspector-general (railway police) Vinay Kumar said a team of forensic experts was sent to Naugachia from Patna to examine the rucksack.
Kumar said the police was searching for a laptop bag belonging to him.
The police is trying to probe gangs operating on the Kathihar-Barauni stretch, which may have links to the case, though without much success so far.
