The stepfather of Mason Pendrous says his stepson's body was only found after a fellow student climbed up over the roof to look into his room.
The 19-year-old's body was discovered last month in the Sonoda Village student accommodation at the University of Canterbury.
- University of Canterbury speaks out after student's shock death
- Former High Court judge to lead investigation into student's death at University of Canterbury
- Head of University of Canterbury vows to leave 'no questions left unanswered' following student death
It was initially believed that his disappearance went unnoticed for around two months, but since then friends have said they had contact from him around a month before his body was found.
The university said at the time it was "inconceivable to imagine how these circumstances could have occurred".
Speaking to RNZ, Pendrous' stepfather Anthony Holland said the family first thought the teen hadn't been in touch due to a busy student life.
However, when Pendrous' mobile phone stopped going to the answer machine and started saying "number not available", the family became concerned.
Eventually, Holland said, the family got in contact with someone living in the same hall as Pendrous who "decided something wasn't quite right".
"To the best of my knowledge, he climbed up over the roof and around, and realised something was wrong, and contacted security, who entered the room," he told RNZ.
A former High Court judge has now been put in charge of investigating the death.
The investigation aims to establish the circumstances around Pendrous' death, whether any concerns about his welfare were made to the university at any time and whether there was a response to any such concerns.
The university's policies and procedures to monitor and respond to student welfare issues at Sonoda Village would also be assessed.
The investigation, which began last week, is expected to take around six weeks.