A former soldier for " his three daughters" had a history of escalating violence, according to his brother.

Travis Decker, 32, has been the target of a large manhunt ever since June 2, when — nine-year-old Paityn Decker, eight-year-old Evelyn Decker and five-year-old Olivia Decker — at a campsite outside Leavenworth, Washington.

Investigators say the girls were visiting their dad during a court-ordered visitation at the time of the killing. An autopsy on Friday determined the cause of death to be suffocation, the sheriff’s office said. The girls had been bound with zip ties and had plastic bags placed over their heads.

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A huge manhunt is now underway to locate Mr Decker as officials and an array of state and federal agencies have searched hundreds of square miles, much of it mountainous and remote, by land, water and air. The US Marshals Service was offering a reward of up to $20,000 (£15,000) for information leading to his capture.

A man - believed to be Travis Decker - was seen near a remote lake by hikers who said he looked ill-prepared for the treacherous rural terrain. The man ran from sight when a police helicopter swooped over the remote area.

His brother has now revealed Travis' 'violent' reaction when his family attempted to hold an intervention. Thomas, 35, told the that his brother tried to resort to violence during one family incident.

Thomas found out that Travis was starting to abandon his family when he and his partner Whitney were beginning the divorce process. He said: "I told him, 'You can't leave your family like this. People get divorced all the time, if you are not happy in your marriage, that's okay."

In a desperate bid to help Thomas and his father staged an 'intervention' with Travis at his house. He said: "We had hoped to have a good conversation with him - to ask him if he needed anything, any help, financial or otherwise. We are family, we want to help him and see what we could do to get him back on track.

"'But things did not go well, he tried to resort to violence, because we were not supposed to be there and we just showed up unannounced,' said Thomas, who refused to elaborate further but clarified there was no physical violence."

Thomas added: "The guy on the wanted poster for murdering my three nieces is not the brother I know. I can't even comprehend what is going on. I am in complete shock that he would do something like this. He loves his daughters – at least I thought he did. And Whitney is devastated beyond belief."

A page set up to help the girls' mother raised more than $1.2 million by Wednesday afternoon.