The 52-year-old Singh, who was the State President of Cooperative Cell of UPCC, was shot dead by unidentified persons in Sidhari area when he had gone for a morning walk, on December 19, they said.
Singh had contested the state Assembly election on Congress ticket in 1993 from Lalganj Assembly segment, police said.
The victim's wife had lodged a complaint against Yadav alleging that he was involvement in the conspiracy to kill her husband.