South Australian prisoners will help investigate cold case murders with playing cards, and could have their sentences reduced if they help solve a crime.

Prisoners will be given cards with photos and details of more than 100 unsolved murders, some up to 50 years old, and will be able to speak with cold case investigators.

Inmates could receive sentence reductions, witness protection and financial incentives in return for information that leads to cases being solved.

Detective superintendent Des Bray says it is a logical initiative.

“There is evidence that targeting people in custody for information has proven to be an extremely successful strategy in solving murders,” he said on Thursday.

“Close to 6,000 people pass through our prison system each year. Of those people, someone knows something, or they know someone who knows someone.”