Sevdet Besim was arrested in Melbourne last year when he was 18 and accused of planning to run down police officers with a car, behead them and then shoot other people at an April 25 Anzac Day parade for Australia’s soldiers.
He pleaded guilty to one charge of “doing an act in preparation for or planning a terrorist act”, a Supreme Court of Victoria spokeswoman told AFP, which carries a maximum sentence of life in prison.
A British boy, who was 14 when accused of masterminding the plot via encrypted messages with Besim from his home in northern England, became his country’s youngest person convicted of terrorism when sentenced to five years in jail last year.
Australian prosecutors have alleged Besim also had online conversations about using the kangaroo during an attack.
“They have a general discussion around animals and wildlife in Australia including a suggestion that a kangaroo could be packed with C4 explosive, painted with the IS (Islamic State) symbol and set loose on police officers,” the Australian Broadcasting Corporation reported, citing court documents.
Canberra has been increasingly concerned about home-grown extremism and raised the terror threat alert level to high in September 2014.
Authorities have conducted a series of counter-terrorism raids in various cities, while the government has passed new national security laws.
Besim is due back in court in August.