Ms O’Shea, who lived in Melbourne, was visiting her son Alan O’Shea in Ravenshoe for the birth of her grandchild when she disappeared from Atherton on December 29, 2005.

On the morning of her disappearance Ms O’Shea told a friend she was going to walk into the Ravenshoe town centre, and her son Alan would pick her up.

He picked her up and drove her to Atherton around midday. His mother told him she was going to play pool at the Atherton Hotel and would make her own way to visit a friend in Mareeba.

Her family reported Ms O’Shea missing by family on January 13, 2006.

Atherton CIB detectives’ investigation into Ms O’Shea’s movements revealed she attended the bottle shop at the Atherton Hotel on the night of December 29 and left in the company of two men.

Police investigations into Ms O’Shea’s disappearance are ongoing and detectives believe a person, or persons are responsible for her death.

A 2014 coronial inquest into Ms O’Shea’s disappearance found she likely died soon after December 29, 2005, in the Tablelands area.

“There is no evidence that Ms O’Shea was seen anywhere after she left the Atherton Hotel and it is to be expected that, had she travelled elsewhere after being at the Hotel, sightings of her would have been reported.

“The cause of her death cannot be determined but it is most likely that an unknown person or persons with whom she came into contact either at the Atherton Hotel or soon after she left there, caused her death and disposed of her body,’’ Coroner Jane Bentley found in 2014.

Ms O’Shea’s children Daniel O’Shea and Lily Parmenter appealed to the public come forward with information about their mother’s suspected murder

They said her disappearance was out of character and had left their family devastated.

“It’s been eighteen years since Mum was last seen and to this day there’s been no real answers or leads. Mum was a fun-loving, happy go lucky person who had such a positive outlook on life and for her to go missing the way she did is definitely out of character.

“Her disappearance has brought a lot of trauma to the family and hopefully this $500,000 reward will solve this case once and for all,’’ Mr O’Shea said.

Ms Parmenter said her mother always made her children her “first and last priority”.

“She was the glue that held us together…losing her has been the worst thing that’s ever happened to any of us. We are hoping the reward will help incentivize someone with information to come forward what they know.

“With any luck we’ll be able to get closure that we need bring mom home and to bring the perpetrators to justice. Katie O’Shea was an amazing woman and an even better mother… no one has the right to take another life and they need to be held to account,’’ Ms Parmenter said.

Lead investigator Detective Senior Sergeant Brett Devine said Ms O’Shea’s disappearance was suspicious and there are people “who know what happened”.

“Kathleen’s disappearance was out of character; she was in Far North Qld pending the arrival of her first grandchild. We know that Kathleen was very excited to be a grandmother and intended to be present for the birth,” Detective Senior Sergeant Brett Devine said.

“A $500,000 reward is now in place for information that may lead to the conviction of the person or persons responsible for Kathleen’s disappearance. Any information no matter how small or insignificant it may seem, could be the key to bringing closure for Kathleen’s family,’’ Detective Senior Sergeant Devine said.

Police Minister Mark Ryan said he hoped the reward provides answers for Ms O’Shea’s family, friends and the far northern Queensland community.

“Police will not stop until they find the answers her loved ones deserve,” Mr Ryan said in a statement.