"While the Coroner will determine the exact cause of death, it appears Mr Black dropped his car keys down the stormwater culvert and had attempted to retrieve them," Mr Basham said.
"Police recovered a set of keys in the stormwater culvert belonging to the deceased, as a result of a thorough scene examination."
Mr Black, 43, was a welder at Wellington firm Metal Construction, where he had worked for up to 10 years. He and his long-term partner, Melanie, had separated several weeks earlier.
Company owner Ian Vibert said 23 staff worked at the tight-knit firm, but "there's not many people at work today" because they were too shocked and upset.
Mr Black, a welder, had loved socialising with his colleagues and often had them over for barbecues. He was also a leader at the company and helped train "all these younger whippersnappers".
"He was a bit of a character. He loved his Stetson hat and he's got long, flowing blond hair and cowboy boots," Mr Vibert said.
"He was a bit of a horseman in his day."
Mr Black was also "ultra-intelligent".
"He was probably wasted being an engineer. He should have probably been more into IT or something. He was a bloody wizard on the computers [and] he did help us a lot ...
"He was a good problem solver but he just loved his work. He just loved bashing the steel around and welding and carrying on - it was just a thing he loved to do whereas he could have probably earned twice as much money being in computers.
"But you've got to follow your loves and whatever your desires are."
Mr Vibert suspected it was Mr Black whose body was down the drain when he learned his work van, with its distinctive "Welder" plate, was found nearby. His suspicions were effectively confirmed when he went to Mr Black's home but was unable to raise him.
He speculated Mr Black had probably been taking in the Courtenay Place "hum" on Friday night before accidentally dropping his keys down the drain, which police believe happened about 6am on Saturday.
"I guess any other person probably wouldn't have even attempted to lift the grate up to retrieve his keys ... but him being a bit of a tradie with structural steel and heavy metal, we wouldn't think twice about lifting up a grate to see if we could get our keys back," Mr Vibert said.
"It's bloody horrible ... being trapped in a confined space trying to maybe get yourself out. I don't want to think about it."
A Wellington City Council spokesman said the stormwater drains were covered by hinged, heavy-duty cast-iron grates.
"We don't know the exact circumstances of how this person ended up head down in the sump but we are confident it was a freak occurrence," he said. "No one can remember anything like this happening before."
Police were examining the grate but it was unlikely the incident would lead the council to "undertake any additional measures to our normal processes".
Flowers have been placed at the drain, which has been covered and cordoned off by road cones.
