Qld mum's murderer from Cairns: police

Queensland police have honed in on who they think killed Cooktown mum Donna Steele but still need more information to make an arrest.

Detective Inspector Damien Hansen said on Friday investigators had identified a person of interest.

He said they were not from Cooktown and could have been travelling through the small town from Cairns, but would not speculate on whether they came there specifically to kill the mother-of-two.

The 42-year-old was last seen at the town's IGA supermarket on August 2.

Her body was found four days later in the nearby Endeavour River.

Police are continuing to appeal for people who were in the far north Queensland town on August 2 and who have information on the case to come forward.

Det Insp Hansen said people who were loyal to the killer hadn't told police the full story of what they knew.

"We believe that people in Cooktown have knowledge and are covering for that person," he said.

"I'm encouraging those people it's never too late - come forward, give us that information now."

The revelations of a person of interest come one week after Queensland Police Minister Mark Ryan issued a $250,000 reward and indemnity for those not directly involved with Ms Steele's death.

The reward is still available.