He was named as Martin Bryant, 28, from Hobart; he had no criminal record but a history of psychological problems. Police said the death-toll of 34 could rise; victims ranged in age from three to 72 years. Bryant was arrested after fleeing a burning guesthouse where he had held three hostages.
He left with his clothes ablaze after an outbreak of fire ended an 18- hour siege. Detectives had tried to persuade him to surrender peacefully. Negotiations ended when the battery of his phone went dead. He ran from the building and threw down two rifles after his clothes caught alight. Last night he was in the Royal Hobart Hospital, which was also caring for 18 of his victims.
The police have not yet interviewed Bryant nor established a motive for the attack. Local media said he had mental problems and mood swings after a car crash three years ago. Former neighbours said at the farm he lived on near Hobart he had threatened to shoot trespassers and terrified locals with his fondness for firearms. He had bizarre habits and was said to sleep with a pig.
A former neighbour said Bryant's father drowned at a dam on the property about three years ago. The death was declared a suicide but the neighbour said Bryant's reaction was strange: "I don't think he was at all upset".
He holed up in the Seascape Cottage on Sunday after running amok in a rampage which left bodies strewn around Port Arthur, one of Tasmania's most popular tourist attractions, the ruins of the penal colony to which Britain sent many prisoners from 1830 to 1877.
The victims included a three-year-old girl, her six-year-old sister and their mother. The six-year-old was cowering behind a tree when she was shot.
At the guesthouse, police found the remains of two of the hostages, believed to be David and Sally Martin, who owned it, and who were apparently friends of Bryant's father. A third hostage was still missing.
The Tasmanian Assistant Police Commissioner, Luppo Prins, said: "The 28-year-old man is currently at the hospital under guard of police and it is proposed to talk to him as soon as possible." No charges have been laid yet.
As Tasmanians flocked to a special service at Hobart's Anglican cathedral last night, the Australian Prime Minister, John Howard, said a culture of violence might be taking hold in Australia; the killings had "shaken the nation to the core".
The gunman's rampage began when he entered the Broad Arrow Cafe in Port Arthur, carrying a bag from which he pulled a rifle and started shooting: 20 people died. He moved on among ruins of the convict settlement, shooting dead four people before driving to the entrance, where he killed the mother and her two daughters. He shot dead all four occupants of a car which he drove to a service station, where he killed a woman, his 32nd victim. Four foreigners were among the dead - two Malaysians, a New Zealander and another from South Asia, or South- East Asia.
At the service station Bryant kidnapped a man and shoved him in the boot of the car, and then drove to the nearby Seascape guest house.
Yesterday, as shock swept Australia, Mr Howard called a summit next week of federal and state government ministers to tighten gun-control laws. "I will not retreat an inch from the national responsibilities I have on this issue," Mr Howard said.