Prime Minister Kevin Rudd, visibly upset during a television interview, reflected the country's disgust at the idea that arsonists may have set some of the 400 fires that devastated Victoria state, or helped them jump containment lines.
"What do you say about anyone like that?" Rudd said. "There's no words to describe it, other than it's mass murder."
The country's top law officer, Attorney General Robert McClelland, said that people found to have deliberately set fires could face murder charges. Murder can carry a life sentence.
More than one dozen fires still burned uncontrollably across the state, though conditions were much cooler than on Saturday, which saw record-high heat and winds of up to 60 mph (100 kph).
At least 750 homes were destroyed on Saturday, the Victoria Country Fire Service said. Some 850 square miles (2,200 kilometers) of land were burned out.
Officials said both the tolls of human life and property would almost certainly rise as they reached deeper into the disaster zone, and forecasters said temperatures would rise again later in the week, posing a risk of further flare-ups.
Police updated the death toll late Monday to 135.
In a sign of the nationwide impact of the tragedy, Parliament suspended its normal sessions Monday to hear condolence speeches by legislators. The voices of many quavered with emotion. Some called it Australia's worst peacetime disaster.
Victoria Police Commissioner Christine Nixon said investigators had strong suspicions that at least one of the deadly blazes - known as the Churchill fire after a ruined town - was deliberately set. And it could not be ruled out for other fires. She cautioned against jumping to conclusions.
Police sealed off Maryville, a town destroyed by another fire, with checkpoints, telling residents who fled and news crews they could not enter because there were still bodies in the streets. Armed police moved through the shattered landscape taking notes, pool news photographs showed.
While Australia grapples with wildfires every year, deaths are rare - and unheard of in this number. The country's deadliest fires before the current spate killed 75 people in 1983. In 2006, nine people died on South Australia's Eyre Peninsula.
But on Saturday, the wind surged and changed direction quickly time and again, fanning the blazes and making their direction utterly unpredictable from minute to minute. Local media had been issuing warnings in the days leading up to the weekend, but many people guarding their homes with backyard hoses would have been outside when the wind changed, and thus could have missed the fresh warnings.
Evidence of heart-wrenching loss abounded. From the air, the landscape was blackened as far as the eye could see. Entire forests were reduced to leafless, charred trunks, farmland to ashes. The Victoria Country Fire Service said some 850 square miles (2,200 kilometers) were burned out.
At Kinglake, a body covered by a white sheet lay in a yard where every tree, blade of grass and the ground was blackened. Elsewhere in the town, the burned out hulks of four cars were clustered haphazardly together after an apparent collision. Australian Broadcasting Corp. radio reported a car in a small reservoir, the driver apparently steering there in desperation.
"What we've seen, I think, is that people didn't have enough time, in some cases" Nixon told a news conference. "We're finding (bodies) on the side of roads, in cars that crashed."
John Handmer, a wildfire safety expert at the Royal Melbourne Institute of Technology, said research had shown that people in the path of a blaze must get out early or stay inside until the worst has past.
"Fleeing at the last moment is the worst possible option," he said. "Sadly, this message does not seem to have been sufficiently heeded this weekend with truly awful consequences in Victoria."
Even if a house is set ablaze, it will burn more slowly and with less intensity that a wildfire and residents have a better chance of escape, he said.
Extraordinary survival tales were also told.
Jack Barber described how he fled his house in Pheasant Creek near Kinglake with his wife and spent Saturday night on a sports field dodging flames that licked at them from different directions as wind gusts blew around.
They drove out of the disaster zone to Wittlesea on Sunday.
"There were dead horses, live horses, kangaroos bouncing down the road with flames at their back. It was horrific," Barber said.
Daryl Hogan of Wandong, 12 miles (20 kilometers) north of Wittlesea, said he leapt into his pool to escape the flames as they roared over his house, leaving it unscarred but razing the neighbor's.
Nine Network television reported that one woman, Nesh Sinclair, sheltered with her children in the burrow of a wombat as the worst of the fire passed.
Victoria state Premier John Brumby on Monday announced a commission would be held to examine all aspects of the fires, including warning policies.
"I think our policy has served us well in what I call normal conditions. These were unbelievable circumstances," Brumby said on Australian Broadcasting Corp. television.
Blazes have been burning for weeks across several states in southern Australia. A long-running drought in the south - the worst in a century - had left forests extra dry and Saturday's fire conditions in Victoria were said to be the worst ever in Australia.
In New South Wales state on Monday, a 31-year-old man appeared in court charged with arson in connection to a wildfire that burned north of Sydney at the weekend. No loss of life was reported there. He faces up to 10 years in prison.
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