The manhunt for a father who is believed to have murdered his three young daughters in a crime that shocked the world has taken a grim turn.

Cadaver dogs have been called in as the search for Travis Decker enters its fourth week, with police believing the military veteran may have died.

Authorities have been scouring thick forest in Washington State after the bodies of Mr Decker’s daughters Paityn, 9, Evelyn, 8, and Olivia, 5, were all found with their hands bound and plastic bags over their heads.

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In an update on social media, the Kittitas County Sheriff’s office said that despite a flood of tips, there was no specific evidence that Mr Decker remained alive or even in the search area.

“Seemingly strong early leads gave way to less convincing proofs over the last two weeks of searching. Still, we can’t and won’t quit this search; Paityn, Evelyn, and Olivia Decker deserve justice. And Decker remains a danger to the public as long as he’s at large,” the post read.

It went on, “Some search resources are being redirected to find and recover Decker if he died in the rugged wilderness during this intense search — a possibility that increases every day.

“Visible extra patrols continue in the area. The US Marshals service has turned their fugitive-finding resources to the task of finding Decker if he’s left our area.”

Mr Decker collected the girls for a scheduled visit on May 30 but failed to return them at the agreed time.

Their mother Whitney, who had previously raised concerns about Mr Decker’s spiralling mental health, raised the alarm with police, sparking a large-scale search.

But that ended in tragedy three days later when the girls’ bodies were found at a campground close to their father’s white 2017 GMC Sierra truck at the Rock Island campground in Wenatchee.

During an emotional memorial on the weekend, their Ms Decker spoke of her “incredible” girls.

“I truly hope that the legacy of the girls’ lives lives on in everyone’s heart forever,” she said, before going on to describe a family tradition that she developed with the girls after her divorce called “three feelings”.

That is where, at the end of every day, she would ask each daughter about three feelings they experienced that day and what was happening when they felt those emotions.

“I’m so thankful for the time that I had with the girls. And how the three feelings allowed us to connect when the world slowed down. And it really gave me an inside look into their day,” she said. “I believe doing this with them allowed them to come into the world with open hearts and kindness.”

“I hope that you are all able to do some version of the three feelings with your loved ones,” she told the grieving crowd.