All the four are members of Sheru Mian Gang and are residents of Katihar district and they were active in the northeastern parts of the state, Purnia SP Ajit Kumar Satyarthi said.
"This gang recently looted Rs 11 lakh from a maize trader near Rambagh in Purnia and they have confessed to their crime," Satyarthi added.
The driver of the manager of a local Axis Bank branch was also involved in the loot and is currently absconding, the SP said.