Australian police say they are powerless to prevent the circulation of graphic footage of the aftermath of the Port Arthur massacre, posted on YouTube and Facebook.
The footage, taken from a training video stolen from the Tasmania Police archive, was removed from the sites yesterday following complaints.
But the force's deputy commissioner, Scott Tilyard, said unauthorised copies had been made years ago, and it was "all but impossible to ensure that these images are not posted on and circulated via internet-based technologies".
The nine-minute YouTube video, showing close-ups of some of the 35 people shot dead by Martin Bryant at the Tasmanian penal settlement in 1996, was uploaded by an account-holder with the alias FreeMartinBryant. His user profile features numerous other videos outlining conspiracy theories about Australia's worst gun rampage and questioning Bryant's guilt.
Security was increased at Tasmania Police's archive facilities in 2004 after a leaked copy of the video was found on sale at a second-hand shop in Hobart. Police Minister David O'Byrne said it was not believed that a second theft had taken place.
The re-emergence of the footage has traumatised massacre survivors and relatives of victims, for whom painful memories had already been reawakened by the shooting spree in Norway last weekend.
He said when the video was made security was not so stringent, as internet technology was less advanced and mass circulation sites did not exist. High-security storage and access arrangements had since been introduced for all Port Arthur-related material, but "once something goes out there on to the internet, you just totally lose control of it".
Bryant is serving 35 life sentences in the psychiatric wing of Hobart's maximum-security Risdon Prison. His trial judge ordered that he never be released.
A massacre survivor, Peter Crosswell, told the Hobart Mercury: "It's simply terrible and disgusting that these people would be so insensitive as to casually dredge up something many of us would rather forget."
The Tasmanian Premier, Lara Giddings, called the posting of the footage a "callous, disgusting" act.