It was an unseasonably warm autumn afternoon in Sydney. As the temperature nudged 25C earlier on Saturday, Bondi Beach was thronged with sunseekers enjoying the first day of the school holidays.

Just over a mile away at the Westfield shopping mall in Bondi Junction, thousands of people were taking advantage of its seven air-conditioned floors to enjoy some retail therapy.

At about 3.20pm local time (6.20BST), a 40-year-old man, wearing the green and gold jersey of the Kangaroos, Australia’s national rugby league team, stood among the shoppers.

Parents, holding the hands of young children as they window-shopped, were captured on mobile phone video walking within feet of him.

They had no idea their compatriot — Joel Cauchi, from Queensland — was carrying a 30cm-long