Sean Cole, 26, was snatched by a crocodile and dragged under the water Saturday as he and a friend were swimming in the Mary River during a birthday party.
Northern Territory wildlife ranger Tom Nichols said Cole's body and that of a 4.7-meter-long (15-foot, 5-inch) crocodile floated to the river surface early Monday. The crocodile was one of four that rangers shot in the hours after the attack.
"We believe that croc was responsible," Nichols said, though he noted that further tests to match the bite marks on Cole's body would be conducted.
Cole had been celebrating a friend's birthday at the Mary River Wilderness Retreat, an Outback tourist destination 70 miles (110 kilometers) southeast of the Northern Territory capital of Darwin.
Nichols said Cole, an information technology professional from Darwin, either died of chest injuries or drowned as the 650 kilogram (1,430 pound) reptile dragged him under in a disorientating crocodile maneuver known as a death roll.
Moments after the attack, witnesses saw the crocodile swimming upstream with Cole's body still in its jaws, Nichols said.
Police Senior Constable Wade Rodgers, who coordinated the weekend search, said a report on the tragedy would be prepared for a coroner's investigation.
The river is infested with crocodiles, and officials said that as locals the men would have known that.
"They just did something silly," Nichols said.
Crocodile expert Grahame Webb, a Darwin zoologist, said he would not give a swimmer an even chance of crossing the 80-meter-wide (260-foot-wide) river.
"Someone swimming in an area with crocs like that ... crocs are going to zero in on them almost every time," Webb said.
Mary River Wilderness Retreat manager Erin Bayard said the resort has several signs prohibiting swimming. Guests are advised not to go within 5 meters (16 feet) of the water's edge because of the risk of large crocodiles lunging from the river to drag people in.
Crocodile numbers have exploded across Australia's tropical north since the species was protected by federal law in 1971. The crocodile population is densest in the Northern Territory and is promoted as a major tourist attraction.
Last November, a crocodile killed a 7-year-old girl as she swam in a Northern Territory waterhole at a remote Aboriginal settlement and a 9-year-old boy was killed two weeks later by another crocodile at a Northern Territory beach.