Police believe the victim had been keeping the wild kangaroo as a pet.
There are legal restrictions on keeping Australian native fauna as pets, but the police media office said on Tuesday they had no information to make public regarding whether the victim had a permit.
Tanya Irwin, who cares for macropods at the Native Animal Rescue service in Perth, said authorities rarely issue permits to keep kangaroos in Western Australia.
"This looks like it was an adult male and they become quite aggressive and they don't do well in captivity," Irwin said.
"We don't know what the situation was; If he was in pain or why he was being kept in captivity and unfortunately ... they're not a cute animal, they're a wild animal," Irwin added.
Irwin said her rescue centre always rehabilitates native animals with the aim of returning them to the wild, particularly kangaroos.
"You do need a special permit to be able to do that. I don't believe they really give them out very often unless you're a wildlife centre with trained people who know what they're doing," she said.
Western gray kangaroos are common in Australia's southwest. They can weigh up to 54kg and stand 1.3m tall.
The males can be aggressive and fight people with the same techniques as they use with each other. They use their short upper limbs to grapple with their opponent, use their muscular tails to take their body weight, then lash out with both their powerful clawed hind legs.
In 1936, William Cruickshank, 38, died in a hospital in Hillston in New South Wales months after he'd been attacked by a kangaroo.
Cruickshank suffered extensive head injuries including a broken jaw as he attempted to rescue his two dogs from a large kangaroo, The Sydney Morning Herald reported at the time.