A gathering will be held at the Trades Hall building in Wellington today to mark the 40th anniversary of the explosion.
Caretaker Ernie Abbott, 64, was killed in the blast after he picked up a suitcase that had been left unattended on the ground floor.
No one has ever been charged with the death, despite police reopening the cold case in 2019.
What happened
On Tuesday, 27 March 1984, Abbott was locking up for the day at the Wellington Trades Hall.
At 5.19pm he picked up a suitcase which had been left unattended for several hours.
The movement triggered a bomb and Abbott was killed almost instantly.
The force of the explosion was considerable and required a detailed scene examination.
Abbott was the sole victim of the attack and despite numerous investigations, police have always struggled to identify a motive for the bombing.
Political motivations
Union leaders claimed the bombing was political.
In an interview with RNZ in July 2019, former union leader Ken Douglas said his view was formed by the politics of the time.
"We'd had really quite intense anti-union activity by the Muldoon government and that was ongoing to a very large extent, we'd had the Tania Harris marches in Auckland against trade unions, so there was a lot of emotions."
Douglas said he believed the bomb was planted against the trade union movement and against the Labour Party.
He said the media had reported the day before that a meeting was being held between the industrial and political labour was taking place that day.
Fears of terrorism
There were fears of more attacks following the bombing, with newspaper reports indicating police and citizens were on high alert.
The next bombing of note was the following year on the Rainbow Warrior.
But until the 2019 Christchurch mosque attacks, New Zealand had never had a large-scale terrorist attack.
Reopening the cold case
An investigation into the bombing was reopened in 2018 by Detective Senior Sergeant Warwick McKee.
On an episode of Cold Case that aired in June 2019, it was revealed that the bomb was a fizzy drink bottle and that petrol was the likely accelerant.
It was also revealed that the suitcase was lined with pages 9, 10, 19 and 20 of the Evening Post from 18 June 1977.
Despite reopening the investigation, the bomber has never been identified and the case remains unsolved.
Lives affected
The bombing had a large impact on the public following the event.
Newspaper clippings from 29 March 1985 reported Wellington City seemed "certain to virtually shut down" on the day of Ernie Abbott's funeral, with widespread shutdowns of industry to show solidarity and protest the bombing.
About 2500 people filled the town hall for Abbott's funeral.
A tree was also planted in his honour in Cobblestone Park which is nearby the Trades Hall Building.
The bombing also saw Abbott's dog Patches injured.
Long after the event, the Dominion Post reported in 2005 that a lead suspect for causing the event Peter Dijkstra had his life ruined by inquiries by detectives into it.
