Chavinath Yadav is suspected to be involved in illegal sand quarrying in Maudwara and Betni villages of the district and the slain official had been running a drive against the racket there, CBI sources said.
Chavinath along with Gulshan Yadav, who is also an accused in Haq's murder and is on the run, are allegedly part of the quarrying racket and both are said to be close to Raja Bhaiya, CBI sources said.
Raja Bhaiya is the fifth accused in the case.
Meanwhile, the CBI team visited Manikpur and Sangrampur villages with relatives of slain village head Nanhe Yadav along with Kamta Pal, the accused in Nanhe's murder.
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As part of its investigation, the team also went to the site where Nanhe's brother Suresh Yadav was killed, sources here said.
Earlier in a major breakthrough yesterday, Police had claimed to have recovered the service revolver of slain Kunda officer.
With his name cropping up in the matter, Raja Bhaiya had resigned from the UP cabinet on March 4.
The Uttar Pradesh government had recommended a CBI probe into Haq's murder and the Central agency had taken over the investigations on March 7.