Car fire killer Rowan Baxter "tried to break" the wrist of his estranged wife after she challenged him about photos of herself she saw in his car in the weeks prior to him dousing her and their children in petrol and setting them alight, according to one of Hannah Clarke's friends.

Key points: Initially, Hannah Clarke had not considered she was in a violent relationship

Initially, Hannah Clarke had not considered she was in a violent relationship Police say the family had domestic and family violence applications put to court and granted

Police say the family had domestic and family violence applications put to court and granted An expert says the fact people knew about Mr Baxter's behaviour shows people are still not comfortable talking about family violence

Details continue to emerge about the abusive and controlling tactics Mr Baxter, 42, waged against his 31-year-old wife Hannah Clarke, also known as Hannah Baxter, in the lead-up to Wednesday's murder-suicide.

Ms Clarke and her children Aaliyah, 6, Laianah, 4, and Trey, 3, died after the family car was torched on a street in the Brisbane suburb of Camp Hill on Wednesday morning.

Police said Mr Baxter was found dead on the footpath with self-inflicted wounds.

Ms Clarke's friend, who did not want to be named, said the mother-of-three showed her a welt on her arm and told her she received it after she challenged him over the photos in front of the children.

The woman said Ms Clarke also previously told her Mr Baxter "controlled every aspect of her life" and had hacked her phone and left old devices around the house to record her conversations.

Ms Clarke told her friend that Mr Baxter "was so obsessed with her it was scary".

She also shared how it was not until she left Mr Baxter and spoke to police that she realised how serious the situation was.

The friend also said Ms Clarke had felt overwhelmed ahead of a court hearing in January.

The ABC understands a domestic violence order was made, which stipulated Mr Baxter had to stay 20 metres away from his estranged wife.

"How many times do we see this happening before taking action?" the friend said.

"We hear the stories and six months later, no changes are made."

Another friend, who said she worked for a domestic violence (DV) service, wrote on Facebook that, initially, Ms Clarke had not considered she was in a DV relationship.

"We talked about the different types of violence including financial abuse, sexual abuse, emotional abuse and you [Hannah] experienced all of them," she wrote.

"The more he [Rowan] convinced the public of the love for his children and you [Hannah], the more he was able to exercise his coercive control by isolating you and manipulating others into perceiving him as being a good partner."

Tributes left on the street where the three children died in the car fire on Wednesday. ( ABC News: Brittney Kleyn )

Stalking a red-flag for domestic violence

When Ms Clarke told her friends her husband had been following her and photographing her movements, that was a red flag.

An expert on domestic violence at the University of Queensland, Professor of Law Heather Douglas, said stalking was linked to family violence.

"Stalking is a very clear risk factor for serious harm and fatalities in the context of domestic abuse," Professor Douglas said.

She said it could be disguised as the actions of an incredibly caring father.

"But in the context of separation and the context of the obsessiveness of it … that would suggest to me that this looks more like stalking." Professor Douglas said.

She said risk assessment tools used by police and domestic violence prevention groups all included stalking as a risk factor.

Friends, neighbours and police concede warnings signs months earlier

The news of Wednesday morning's horrific events shocked and enraged the Brisbane communities where the family were known.

Friends and family members of Ms Clarke posted online calling Mr Baxter a "monster".

But one of Mr Baxter's friends, Erika Yamasaki, was also stunned, believing he would never hurt his family.

"I am lost in this dark day. Both Rowan and Hannah were there for me during my times of darkness … through trials of being in an abusive relationship. And yet we are here now," Ms Yamasaki wrote in a post.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 1 minute 46 seconds 1 m 46 s People gather to grieve and leave tributes to Hannah Clarke and her three children.

She said she tried to help "pull [Rowan] out of his dark place and hold it together".

"He kept telling me he would never hurt them — never — he would say this over and over again … this just rips my heart out and I will never understand." Ms Yamasaki said.

Others who knew the couple and their children told ABC News that Mr Baxter's actions were not a surprise.

Friends and neighbours watched as the relationship fell apart.

Ms Clarke left Mr Baxter late last year, taking the three children with her.

About the same time, the Capalaba fitness business they ran together closed down.

The Capalaba fitness business the couple ran together closed down last year. ( Facebook )

Living alone in their home, Mr Baxter reportedly displayed increasingly frightening behaviour.

Neighbours said there was a "long build-up" before Mr Baxter killed Ms Clarke and their children.

Friends of the couple, who do not want to be named, have revealed the unsettling knowledge that something bad was likely to happen.

They painted a picture of an angry man with a temper. A relationship in decline. Warning signs flashing.

Hannah Clarke's children at the beach. ( Facebook )

Police have now confirmed they had also been involved with the couple on a number of occasions over the past few months.

"We have engaged with both Hannah and her estranged husband Rowan around domestic violence issues … and referred them both to support services," Detective Inspector Mark Thompson said.

He also confirmed the family had domestic and family violence applications put to court and granted.

Failure to prevent family violence a 'failure of society'

"I think every day that [a] woman is killed or a child is killed is a failing of society in some way," Professor Douglas said.

Professor Douglas points to all the chances Australian society might have had.

"We know that separation is one of the most dangerous times in a woman's life," she said.

"We don't know how long this behaviour was going on in this family — there may have been coercive and controlling behaviour happening in this family for a long time by this male partner."

Police have confirmed they had contact with both Ms Clarke and Mr Baxter for months, but Professor Douglas said it was likely that other services might have had a chance to raise the alarm.

"I think it's difficult to expect individuals in the community to intervene," she said.

But she saw opportunities for other services to be armed with the ability to give domestic abuse victims a safe place to raise concerns.

"It's likely she's engaged with hospitals, with schools, in lots of different contexts over this time," Professor Douglas said.

"For example, can we be sure that she's always been given an opportunity to privately talk with her doctors or, potentially, social workers.

"Since she's been separated, has she been to the GP and talked to the GP about the separation?

"Has she told members of the school community? Have they given her any support around this?"

Hannah Clarke, also known as Hannah Baxter, and Rowan Baxter with their three children. ( Facebook )

Family violence is still in the shadows

Patty Kinnersly, the CEO of Our Watch, an organisation that works to prevent violence against women, said if people knew Ms Clarke and her children were in danger perhaps they were still not comfortable talking about it.

"That's still, in some part, in the shadows and we need to keep working hard to bring this out of the shadows, so the community can support women in this situation," Ms Kinnersly said.

She said violence against women started with sexist behaviour.

"What the evidence tells us is that gender inequality is the driver of violence against women and creates an environment where violence is more likely to occur," Ms Kinnersly said.

Family violence could happen to anybody. ( Facebook )

Facebook and social media companies partly responsible

Professor Douglas said Facebook and other social media companies had the ability to track behaviour and recognise risks.

She said with Mr Baxter's behaviour reportedly becoming increasingly like stalking, companies like Facebook should be able to recognise that and report it.

"They [Facebook and social media sites] obviously have no problem taking down photos all the time — they know what's being posted, they manage their sites very carefully — so I think this kind of behaviour could be observed," she said.

"They obviously have lots of resources at their disposal and maybe they should have greater responsibility as a result of that."