Parvez alias Farru, a resident of Uttar Pradesh's Meerut, was arrested on Tuesday night on charges of supplying a countrymade weapon to main accused Hardeep Singh.
Earlier, the NIA had arrested Pahar Singh, Ramandeep and Hardeep Singh in connection with the killing of Gosain, 60, who was shot dead on October 17 last year near while returning from a RSS meeting.
The NIA took over the case from Punjab Police.
During the investigation, it was found that Parvez supplied arms to Hardeep Singh, one of the main accused in the cases related to targeted killings in Punjab during 2016-17, the counter-terror probe agency said.
The agency also claimed that targeted killings were executed as part of an "international conspiracy" whose objective was to destabilise the law and order situation in Punjab and to revive militancy in the state.
The NIA has so far arrested 11 persons in various cases relating to the targeted killings.
The weapons supplied by Parvez were used in several of the eight incidents of targeted killing.
"He was produced before the NIA Special Court in Mohali which granted the agency one-day custody for his interrogation," the NIA said.
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