"The pistol has since been recovered and he is being questioned about his presence at the scene of the crime. So far, he has not been able to give any convincing answers," Inspector General (IG) Kashmir Swayam Prakash Pani said.
A video has emerged in which a bearded man wearing a skull cap was seen near the injured PSO of Bukhari as he was being taken out of the vehicle. As the gun of the PSO, who later died, fell on the ground, this man was seen running away after procuring the weapon.
Pani added that the state police had formed a Special Investigation Team (SIT) under Deputy Inspector General (central Kashmir) V K Virdi to probe the killing of the editor of Rising Kashmir on Friday. Pani also described the killing of the journalist as a "terror attack".
The identity of the other three attackers was being ascertained, the police official said.
Earlier in the day, images of three of three bike-borne men who are suspected to have killed Bukhari were also released by the police. The three pictures showed the three men riding a motorcycle and had their faces covered. CCTV footage had shown three masked assassins escaping with the murder weapon on a motorcycle.
Shujaat Bukhari and his two PSOs were shot dead by outside the newspaper Rising Kashmir's office in Srinagar on Friday. Bukhari was attacked as he boarded his car in Srinagar's Press Enclave while leaving for an iftar party. The killing, two days ahead of Eid, has been widely condemned across the country.