He's been called the Golden State killer and the East Area Rapist and for 40 years he's remained on the loose.

Now the FBI's offering a $50,000 reward in the hope they can finally hunt down the man accused of 12 murders and 45 rapes in California.

"It may push somebody over the edge who knows something and kind of provide us that one tip we need," an FBI spokesman said. 

The mystery man's style was often to attack sleeping couples in their own homes, sometimes killing his victims.

Investigators believe his first attack was in 1976, the last one ten years later.

He's also blamed for more than 125 burglaries.

He's described as white, about five feet ten inches tall, and would now be aged between 60 and 75.