A CCTV camera caught the shooting by six men in Farikor district's Kotkapura town.
Three suspected shooters were caught in Punjab's Patiala district early on Friday in connection with the murder of a Dera Sacha Sauda follower a day ago, police said.
The special cell of the Delhi Police raided Bakshiwala area, about 30 km from Patiala city, around 3 am following intelligence inputs, it said.
One of the suspects, Jitender, has been arrested, while two others are minors, Delhi Police spokesperson Suman Nalwa said.
Pardeep Singh, 37, who was an accused in a 2015 sacrilege case, was shot dead on Thursday morning at his dairy shop in Kotkapura. His security man and another person sustained bullet injuries in the incident.
Canada-based gangster Goldy Brar is said to have claimed responsibility for the murder in a purported social media post. He is the main accused in the murder case of Punjabi singer Sidhu Moosewala, who was shot dead in May.
Punjab additional director general of police (law and order) Arpit Shukla told PTI that all the six shooters involved in the murder had been identified. Four shooters are from Haryana and two are from Punjab. Efforts are on to arrest the remaining three shooters.
The different modules were being handled independently by Brar, an associate of fugitive Harvinder Singh and jailed gangster Lawrence Bishnoi, police said.
Pardeep Singh was on bail in a case of theft of a Guru Granth Sahib copy from Burj Jawahar Singh Wala village in Faridkot in June 2015. He was also an accused in a case linked to torn pages of the Sikh holy book being found scattered in Bargari in the district in October that year.
Pardeep Singh's killing comes days after the November 4 murder of Shiv Sena (Taksali) leader Sudhir Suri in Amritsar. Both the victims had police protection.