The broadcaster reported that Greig died at about 13:45 local time on Saturday, after being rushed from his home to Sydney's St Vincent's Hospital earlier in the day.
Dr Alex Wodak, director of an alcohol and drugs unit at St Vincent's Hospital, in Sydney, Australia, calculates that at least half the inmates in Australia's prisons are injecting drug users, half of whom continue injecting in jail, where they might typically share needles with 100 people in a year.