Although the police refused to identity who Yogesh Raj was, informed sources said he was a Bajrang Dal activist who was part of a mob that attacked Inspector Subodh Kumar Singh on Monday, killing him instantly.
The officer was hit by blunt object and was also shot dead when he tried to reason with the Hindu activists blocking a busy road with carcasses of animals they claimed were of cows.
Additional Director General (Law and Order) Anand Kumar told the media here that "no action will be taken against any policemen till the probe into the incident is completed".
He also dismissed as speculation reports of intelligence failure as "premature" and said everyone should wait for the probe to conclude before arriving at any conclusion.
The state government has formed a special investigation team (SIT) to probe the violence, the circumstances leading to it and to identify the people and organisations involved in the mayhem.
The officer said that a .32 bore bullet was found lodged in the head of Subodh Kumar Singh.
He said a bullet had also been recovered from the body of the dead youth, Sumit, but added that only an autopsy would confirm further details.
The senior official parried questions about the political links of the three key accused who are also said to include an activist each from the BJP and the Vishwa Hindu Parishad.
"I am not aware of any linkages as yet. But yes, Yogesh Raj is the main conspirator in the whole case," he said, adding that he was yet to be arrested.
The police were raiding several places to nab the accused, the official said.
(With inputs from agencies.)