Shawn Adam Newton, 42, is wanted for questioning over the death of 35-year-old Rebecca Jane Gascoigne.

The mother-of-three was found on the Mitchell Freeway on July 15.

Police also believe Newton may be linked to an armed robbery at a fast food outlet on Marmion Avenue in Duncraig just after 8pm on Sunday, as well as other burglaries in the past week.

In the Sunday incident, the bandit was wearing a black balaclava and a blue jacket with a white and red stripe on the arm.

He was carrying a red bag and threatened staff with a firearm before demanding cash and fleeing.

"It is common for people who are actively trying to elude police to commit crimes in an effort to support themselves," Detective Senior Sergeant Dean Bailey said.

Anyone assisting Newton was placing themselves at risk and could face charges, police said.

"We consider him to be extremely dangerous and he is wanted for questioning over serious matters," Det Sen Sgt Bailey said.

Newton is described as being fair-skinned, about 186cm tall, with a medium build, very short dark hair and brown eyes.

He may have a firearm and might have grown facial hair and be using wigs to disguise himself, police say.

Last week, Newton's NSW-based brother, who did not want to be named, said in a video recorded by police that his sibling was not a "mindless animal".

"I'm sure he's scared," he said.

"I'm sure he didn't wish any pain on other people's children."

The man pleaded with his brother to do the right thing by his daughter, who would one day want some answers.

"She may just want to tell you she hates you. But you have to be there for that moment," he said.

Anyone who sees Newton is urged to stay away and call police on 131 444.