"An FIR has been lodged against MP Dhananjay Singh and one Tursa Devi under section 120 B (Criminal conspiracy) of IPC," SP Manjil Saini said.
Two others, Vineet Singh and Bablu Pandey, were booked under section 302 (murder) IPC, she said.
The FIR was lodged after murder of one Anil Mishra (40) yesterday, she said.
Those close to Dhananjay claimed that case was lodged against him due to political rivalry with SP leaders.