Police say they are speaking to the traumatised other members of the hunting party, including the person who fired the shot that killed Mr Vanderley as he was walking on a hillside trying to find a deer.
No decision has yet been made on laying charges.
Ajax Building Contractors director Greg McIntosh, who took on Mr Vanderley as an apprentice builder eight years ago, said he was "a hell of a nice guy".
"He got on with everyone. He had a huge future in front of him. It's just a tragic loss of life, he was in his prime," he told APNZ.
Mr Vanderley was into "anything outdoors" and liked to take out his own jet boat.
"He was into his rugby, loved his hunting, duck shooting, jet boating - jet boating was a big part of his life."
His family and partner were coping with his death "as you'd expect".
"It's a tragedy for everyone involved."
Mr Vanderley had worked with Mr McIntosh for eight years.
"He did his apprenticeship here and then became a leading hand, and went on to become a foreman with us - a very good tradesman."
He had recently moved to the Palmerston area and was looking at working on his father's farm and doing some building work.
On April 7, Cam McDonald, 29, was shot and killed by another hunter in Wairarapa's Aorangi Forest Park, and in December, Dougal Fyfe, 23, was shot dead near Wanaka by friend Reuben Burke, who mistook him for a deer.
Briton Ian Purchase, whose son Matthew was shot at point-blank range in the back of the head while rabbit hunting in the Waikato in 2007, said: "It does seem quite extraordinary that this keeps on happening in New Zealand and we do feel for all the families who have lost loved ones."
His son, then 22 and an agricultural student in New Zealand on an exchange, needed brain surgery and was in a critical condition for weeks.
Matthew Purchase has since been making a remarkable recovery, his father said.
"Quite amazing when you think back to his initial prognosis, and we are not quite sure how he has been able to do it - I don't think his doctors are, either."
The Mountain Safety Council says that of the 12 people killed in the past 12 years in deer hunting mishaps, 10 were shot by others in their own hunting parties.
The manager of the council's firearms and hunter training programme, Mike Spray, said failure to properly identify the target seemed to be a common factor in all cases.
Sometimes "buck fever" took over logical thought, and hunters just assumed they were firing at a deer.
"It is adrenalin buzz. But these emotions have got to be controlled."
VICTIMS OF HUNTING
* Mark Vanderley, 26, was fatally shot while spotlight-hunting for deer in Southland.
* On April 7, Cam McDonald, 29, was shot and killed in Wairarapa's Aorangi Forest Park.
* In December, Dougal Fyfe, 23, was shot dead near Wanaka.
* Matthew Purchase was shot in the back of the head in the Waikato in 2007. The UK agricultural student needed brain surgery and was in a critical condition for weeks.
- additional reporting: APNZ
