"No person has been arrested yet. However, over a hundred people have been questioned in raids conducted in Delhi, Bijnor and Aligarh," Ahmed said here.
He said many of those who have been questioned had provided "valuable" information about the incident which will play an important role in solving the case.
"There is no time limit fixed for the investigation but the truth will come out soon," he said, adding the police is questioning all the suspects named by the family members of the National Investigating Agency (NIA) officer.
The DGP said Anti-Terror Squad (ATS), Special Task Force (STF) and with NIA are jointly investigating the case.
He also visited the spot in Sahaspur area where the officer was killed.