The name of 44-year-old former UP minister Raghuraj Pratap Singh alias Raja Bhaiya, who has a criminal record and has been jailed in the past, figures in the FIR lodged by the slain officer's wife Parveen Azad in which he has been accused of criminal conspiracy. Parveen had also demanded a CBI probe.
Haq, posted as circle officer in Kunda, was allegedly killed by a mob in Pratapgarh when he had rushed there after village head Nanhe Yadav was shot dead over a land dispute.
The village head's brother Suresh also died of gunshot wounds.
Raja Bhaiya, who resigned from the UP Cabinet after his name cropped up in the case, has refuted the charge.