John Burrows, 58, was killed in an explosion as he approached the rear garage of his mother's property in Wolgan Street, Portland, about 6.30am on Friday, July 24.

Police located the remains of an improvised explosive device (IED) which had been placed outside the garage and believe that Mr Burrows was the intended target.

Mr Burrows' death is an ongoing investigation under Strike Force Avail which comprises detectives from Chifley Local Area Command with the assistance of the Homicide Squad.

They are now seeking information on a cardboard box and a metal plate which are integral to their investigation.

"We believe the box for a Hills brand sprayer was used to cover or hide the IED from sight," Chifley Crime Manager Detective Inspector Luke Rankin said.

"Police are seeking information from anyone that may have been in possession of a cardboard box that originally contained this sprayer unit, and has since discarded it or given it away.

"These particular Hills brand 16-litre knapsack sprayers were sold in Australia from 2012 - 2014 then updated to a newer model."

Images of a box similar to the one used, as well as an image of a box fragment seized from the scene, have been released by police.

They have also released an image of a cast metal place which had formed part of the IED.

It is believed a second similar plate could have been used and was possibly propelled from the site during the explosion.

Police would like to hear from anyone who has seen or found a similar plate.

Finally, detectives are also keen to hear from anyone who has had an amount of black powder stolen or go missing from their property.

Police examinations have revealed black powder was used in the production of the IED, however; its possession in NSW is restricted to only those who hold an appropriate firearms licence.

Det Insp Rankin said this crime had shaken the close-knit community of Portland, and police were doing all they could to ensure someone was brought to justice.

"But we need the community's help," he said.

"If you have any information about why Mr Burrows was targeted, or can assist with information about the sprayer box, the cast metal plate or the black powder, then I implore you to come forward."

Police have urged anyone with information in relation to this incident to call Crime Stoppers on 1800 333 000, or use the Crime Stoppers online reporting page.