An independent investigation is needed to explain the sharp rise in the number of Australian prison deaths being attributed to "natural causes" and the young ages of those dying, according to a Fremantle-based PhD researcher and human rights campaigner.

Deaths from natural causes have become the most frequent cause of death in Australian prisons, consistently outnumbering hanging deaths -- historically the most frequent cause of prison deaths, as Crikey reported last week -- every year since 2001 (except in 2003, when the numbers were the same). Natural causes accounted for almost three in four prison custody deaths in 2008, the last year for which national statistics are available, while 2007 and 2008 logged the highest number of deaths from natural causes since record-keeping began, with 32 and 38 deaths, respectively.