The family of a University of Canterbury student whose body lay unnoticed in campus accommodation for two to four weeks will "never know what he died of", a coroner has concluded.

Mason Drake Pendrous, a 19-year-old commerce student, died between August 26 and September 10 this year, Coroner Sue Johnson found after a special hearing in Christchurch on November 5 to verify when he had died.

England-born Pendrous was found dead by a staff member in his room, number 209 in the Hinoki building of the University of Canterbury's Sonoda Campus in Ilam, Christchurch, at about 10.50pm on September 23.

Today, Coroner Johnson ruled that his death is "undetermined due to decomposition".

"Mason died sometime between 26 August 2019 and 10 September 2019," she said in a finding released today.

"His body was not found until 23 September 2019. The delay in finding Mason's body meant that the cause of his death is unable to be determined. His family will never know what he died of."

Coroner Johnson is still looking into the circumstances of the student's death.

And at this stage, she says she cannot rule out that before his death, Pendrous was ill in his room.

Forensic pathologist Dr Christopher Lawrence performed a full post-mortem examination of Pendrous' body on September 24.

He noted decomposition and saw no injury or obvious cause of death.

There was no evidence of drugs or elevated alcohol levels in his blood and no identifiable pneumonia.

Lawrence stated that although the heart appeared normal he could not exclude some form of cardiac arrhythmia.

And because of the condition of the body it was not possible for Lawrence to assess some infective causes of death like influenza, pneumonia, myocarditis or meningitis.

There was a medicine for gastrointestinal upset in the room and Pendrous' body was found close to a heater which was on and the central heating was turned up, which Lawrence said could be consistent with a fever.

His medical opinion was that the cause of death was undetermined due to decomposition – which the coroner agreed with.

Coroner Johnson said it was "impossible" to know exactly when Pendrous died between August 26 and September 10.

"Given Dr Lawrence's evidence that he cannot exclude infective causes of death, I cannot rule out that before his death Mason was ill in his room," she said.

"This is an issue I will consider during my inquiry into the circumstances of Mason's death."

His death has raised questions about how a young student could go unnoticed and be holed up in his room without any red flags being raised.

An independent probe into the student's death on behalf of the university, overseen by former High Court judge Kit Toogood QC, is ongoing.

Last month's special hearing in Christchurch to verify Pendrous' date of death was told that Pendrous last used his swipe card to get into his university accommodation on August 12.

He was not seen coming or going for a fortnight, during which time his online activity "increased substantially".

The last time he's known to have spoken to anybody was on August 24 when he played an online war game with an old school mate in Wellington where they chatted over headphones.