The manhunt for alleged killer Travis Decker is continuing into its fourth month, as authorities confirm that remains discovered during the investigation are ‘not human.’

Decker has been evading law enforcement since early June after he is suspected of smothering his daughters, Paityn, aged 9, Evelyn, aged 8, and Olivia, aged 5, to death before a planned custody handover with his former wife in Leavenworth, Washington.

Both local and federal authorities have invested months searching the Rock Island Campground in the Okanogan-Wenatchee National Forest, where the bodies of the girls were discovered in Decker’s deserted vehicle.

There had been hope last week of a breakthrough in the case, when Chelan County Sheriff Mike Morrison announced that bones were discovered during the FBI’s extensive two-day search of the campground.

But Morrison has since said federal authorities ‘just said it wasn’t Travis, wasn’t associated with any other cases, not human,’ the Seattle Times reports. 

Still, Morrison said the update is a sign that authorities are making progress in the search efforts for Decker, who remains wanted on charges of first-degree murder and first-degree kidnapping.

‘I think it just further shows that we’ve done a thorough search of the area,’ he said, adding that the sheriff’s office will now ‘continue to expand out and search additional areas when we have resources available.’

Another federal agency will be coming in this month to help out with those efforts, Morrison said, though he declined to specify which one. 

Meanwhile, authorities will continue to examine whether other items collected during the operation may be connected to the case, Fox 13 reports.  

Despite the ongoing efforts to track down the murder suspect, it remains unclear whether Decker is still alive and on the loose.

Police have noted that the 32-year-old has extensive wilderness survival training as an Army veteran and member of the Washington National Guard.

Yet Morrison insisted last month that investigators ‘have not given up’ on finding him.

‘We understand the frustration, we feel it as well,’ he said at a news conference.

‘We will not relent, we will not give up until Travis Decker is taken into custody.’

‘This is not going to go away until Travis is located, whether he is alive or not,’ the sheriff continued, as he expressed doubts about the former soldier’s ability to survive in the wilderness this long despite his military survival training.

‘He has to be perfect every single day,’ Morrison explained. ‘We just have to be perfect once.’

Police have said Decker was suffering from mental health issues and had recently been diagnosed with borderline personality disorder.

He was homeless and living out of his car by the time he picked up his three girls from their mother’s house on May 30.

Decker had even court-mandated to receive mental health treatment and domestic violence anger management counseling but had refused.

By the time the girls had disappeared, the Washington National Guard had been in the process of filing a disciplinary discharge against Decker due to his repeated absences.

Yet Decker’s ex-wife Whitney told police she didn’t believe Decker was dangerous, and that he loved his daughters, with whom he had a ‘good relationship’.

The US Marshals Service is offering a reward of up to $20,000 for information leading to Decker’s capture.