Australian law enforcement authorities today announced that the New South Wales student accused of documenting plans in a notebook to assassinate two senior Australian politicians is the nephew of a Sri Lankan cabinet minister.

The ABC revealed Mohamed Nizamdeen, 25, is related to Sri Lankan MP Faiszer Musthapha, who is the country's Sports and Local Government Minister.

The PhD student,, is also the grandson of Jehan Kamer Cassim, the late former chairman of one of Sri Lanka's biggest banks — Bank of Ceylon.

Nizamdeen, who also worked as a UNSW business systems analyst, was arrested at the Kensington campus last Thursday.

His arrest came after a colleague found a notebook allegedly containing details of plans to kill former prime minister Malcolm Turnbull and his deputy Julie Bishop.

The alleged list of targets also included the former speaker Bronwyn Bishop, the Sydney Opera House, major train stations and police stations across the harbour city.

On Friday police told a media conference Nizamdeen appeared to be an Islamic State affiliate.

Mithra De Alwis, a friend of Nizamdeen's brother, Kamer, today posted a message on Facebook on Kamer's behalf, describing Mr Nizamdeen as "an open minded Muslim" who he believed was innocent.

"He would have had absolutely no reason to engage in such disgusting, hateful crimes to a city, which has been extremely opening to him for the past six years," he said.

"He has not been able to communicate with any one of us back home and we are simply broken and deeply affected by this unnecessary turn of events."

Plain-clothed detectives seized computers, mobile phones and documents from Nizamdeen's inner-city apartment at Zetland on Friday before conducting further raids on university grounds.

Police allege Nizamdeen, who does not have any criminal history in Australia, was operating by himself, but do not believe he was capable of carrying out a terror attack.

The commerce graduate was one of the faces of UNSW's Hero Program and had worked as a business systems analyst since 2016, where he helped develop several projects aimed at stopping identity theft.

While his student visa is due to expire at the end of this month, the Australian Federal Police have applied for a Criminal Justice Stay visa so they can prosecute him in Australia. (With inputs from ABC)