Thirteen years after Jim Donnelly's disappearance, it is still not clear whether it was an accident, a suicide, a murder or a staged death.
For the past five months, Three's The Project has been investigating the disappearance, which is one of the most mysterious in New Zealand's history.
The last known sighting of the Auckland father was at work, before he disappeared from the Glenbrook Steel Mill with no explanation.
Five days after his disappearance, his hard hat was found at the mill resting next to a deep vat filled with acid.
Inside, his work glasses, credit card and cash were discovered. His work key was also discovered - however Mr Donnelly's wife, Tracey, says it had been removed from the rest of his keys, which have never been found.
It's a gruesome thought - but could his body have been in the acid tank alongside his belongings?
Chemistry professor Allan Blackman from Auckland University put it to the test.
Watch the video for The Project's full report.
