The matter has been handed over to the Crime Branch, where a separate team has been formed to probe the incident.
The policeman was beaten up when MLA Kshitij Thakur moved a privilege motion against being stopped for speeding.
The MLAs involved in the attack have been identified and an FIR has been filed.
The Congress leader met the family of slain DSP Zia-ul-Haq at his native village and extended his condolences.
Raja Bhaiya, the MLA of Kunda, has been named as the main accused in one of the four FIRs.
While the first FIR relates to the killing of the DSP, two others are on the murders of the Gram Pradhan Nanhe Yadav and his brother.
The IGP of Uttar Pradesh, Rajkumar Vishwakarma, said a single bullet killed Deputy Superintendent of Police Zia-Ul-Haque.
One FIR will be regarding the murder of the DSP on the basis of his wife's complaint to the UP Police.
The government doctors citing his post-mortem report say the DSP should have been taken to hospital within 30 minutes of being shot.
Akhilesh Yadav said all demands made by the wife of the DSP Parveen Azad with regard to the investigation have been accepted.
Uttar Pradesh Chief Minister Akhilesh Yadav met the families of two others killed in Kunda along with the Deputy SP.
Meanwhile, Additional DGP of the area, Arun Kumar, has ruled out arrest of former minister Raja Bhaiya.
Haq's wife had earlier threatened to commit suicide if a CBI probe was not ordered into her husband's murder.
Raja Bhaiya, who resigned as a UP minister on Monday, demanded a CBI probe into the murder of DSP Zia-ul-Haq.
Samajwadi Party chief Mulayam Singh Yadav confirmed that Chief Minister Akhilesh Yadav has accepted Raja Bhaiya's resignation.
Controversial Uttar Pradesh politician Raja Bhaiya was booked for the murder of the Deputy Superintendent of Police.
Tapas Chowdhury, a sub-inspector attached to the special branch, was shot from close range while trying to control the clashing students.
The judge rebuked the policeman saying, "You are sitting in front of me since morning..You could have prepared for deposition."
The policeman was denied leave after working for over 30 hours since late on Friday, a police official said.
A traffic sub-inspector flung his lathi in an effort to stop a speeding biker but it hit the old man who sustained head injuries.