Police have begun interviews with bystanders who witnessed the shooting that took place on Thursday at the Boroko Foodworld in Port Moresby.
Although a motive is yet to be established, according to latest police investigations, 9mm Glock pistols were used by the two foreign (Filipino) guards (a supervisor and his subordinate) during the time of shooting.
Police also say both were employees of Dragon Security.
The foreign guard supervisor was shot dead while the other Filipino is in police custody.
Furthermore, two nationals (both children) sustained injuries from fragments of the bullet and were hospitalised.
Police say the users had permits but whether the firearms were registered or not; that will be established during the course of the investigations.
Police are currently working with the Philippines Embassy, Boroko Foodworld and the security firm and other relevant authorities to dig further into the investigations.
Meanwhile, the foreign suspect has been charged and arrested for one count of wilful murder.
Police say more charges will be laid as investigations continue.