Meanwhile, an ABC News investigation revealed that Nugent had previously shared pro-Gaza content and criticized Israel on social media, but it is unclear if this motivated his attack on Haines.
Rod Nugent, the father of 43-year-old Brenden Nugent, and Rod's partner, Christine Cunningham, have been "family friends" with Australian politician Helen Haines "for more than 20 years," they told the press on Tuesday.
Brenden Nugent is suspected of deliberately targeting Haines in a car ramming attack outside her office on Monday.
Rod Nugent and Cunningham added that they will be "assisting Victoria Police in any way we can."
Brenden Nugent has been arrested and charged with dangerous driving causing serious injury, intentionally causing serious injury, and the Commonwealth offense of causing harm to a Commonwealth public official, BBC News reported.
He is due to appear in Wangaratta Magistrates' Court on Wednesday, BBC added.
Haines was taken to hospital and underwent surgery overnight between Monday and Tuesday. She is reported to have lost one of her legs, with doctors working to save the other, unidentified sources told Australian media.
Australian Prime Minister Anthony Albanese told the public broadcaster, Australian Broadcasting Corporation (ABC News), that "It's clear that there was a deliberate act here. This wasn't an accident; someone was just skidding off the road."
Haines is in a "critical but stable" condition, Albanese told ABC News.
Home Affairs Minister Tony Burke told ABC News that witnesses said the alleged attacker reversed the vehicle and struck Haines a second time before a bystander intervened.
Nugent previously shared pro-Gaza content, criticism of Israel
Meanwhile, an ABC News investigation revealed that Nugent had previously shared pro-Gaza content and criticized Israel on social media in recent years.
An investigation by ABC's fact-checking unit found that he had also shared fundraising campaigns for Gaza. He was also active for years in environmental causes, particularly campaigns opposing deforestation.
However, the investigation also found that Nugent had previously praised Haines for her climate positions.
According to ABC News, investigators found the direct comments Nugent made to Haines contained no expressions of anger or malice toward her.
Nugent was held in custody overnight and questioned on Tuesday morning.
ABC News reported that he was known to police and had undergone a mental health assessment. Counterterrorism officials were also participating in the investigation, although the motive remained unclear.
At this stage, there is no basis to conclude that Nugent's posts concerning Israel and Gaza motivated the attack on Haines.
Reuters contributed to this report.