Greens senator Lidia Thorpe has been met with a sea of criticism after appearing to endorse a protest at Old Parliament House, where the doors of the historic building were set on fire.
The blaze burnt the front doors of Canberra's heritage-listed building, causing "tragic" and potentially irreparable damage according to Museum of Australian Democracy director Daryl Karp.
Thursday's fire broke out amid a protest at the entrance and also caused extensive damage to the portico.
Police confirmed officials had agreed a small smoking ceremony could take place as part of a peaceful protest but said it got "a little bit out of hand".
The Australian Federal Police on Friday announced a joint taskforce with ACT Policing to identify the protesters responsible for the blaze.
Senator Thorpe retweeted footage of the fire and wrote "Seems like the colonial system is burning down. Happy New Year everyone". The tweet has since been deleted.
Deputy Nationals leader David Littleproud said the reaction was "disgraceful".
"For politicians to sit there and encourage this, it is not responsible, it is disgraceful, and they should consider their position in the Australian parliament," he said.
Labor MP Mark Butler said Senator Thorpe - and the entire Greens party - had "absolutely crossed a line".
"It was an outrageous, disgusting level of support given to what appears to be a criminal act ... she should be utterly ashamed of herself," he said.
"(Greens leader) Adam Bandt today needs to stand up and be very clear with the Australian people what action he is taking to distance the Australian Greens from a position that they appear to have taken yesterday."
Mr Bandt was contacted for comment but a media representative pointed to a tweet from Thursday, where Mr Bandt labelled the protest "a terrible sight".
"The Greens don't want to see the planet burning or Old Parliament ... if this was arson, it's unacceptable," he said.
Social media footage shows police dragging protesters away from the front steps of the building and a large fire burning at the doors.
Detectives from the newly-formed Taskforce Pike have used CCTV footage from parliament and surrounding premises as well as body-worn camera footage to identify several suspects who will be interviewed.
Offences being investigated include damaging Commonwealth property and arson. The maximum prison sentences are 10 and 15 years respectively.
Aboriginal Tent Embassy activists distanced themselves from the protest, saying a smoking ceremony that took place did not have knowledge or consent from the Embassy Council.
Another fire was started by protesters near the building on December 21.
Ms Karp told the ABC closing due to "violent protests" was "really tragic".
She said further examination was needed to determine if damaged parts of the heritage-listed building could be fixed, with the doors "pretty damaged" and the portico "really burnt out".
"The portico was built specifically for the Queen's visit in the '50s and so it has substantial significance, as do the doors which are from 1927," she said.
"It's unclear whether we can restore the doors or not. Obviously they are pretty significant collection items and that's a really big one for us."
Ms Karp said the lower gallery floors had original lino covering from 1927.
"It's got a lot of soot and a lot of water on it so we will need to check it is still okay."
ACT Policing has launched an investigation into the blaze, noting while there were no injuries there was "extensive water damage" to the building's interior.