Could a mod please change Corinna's name in the title? The iPad autocorrected it twice and I changed it, but it must have stubbornly done it a third time . I am not able to edit the title.

South Australian police are investigating possible links between two of Adelaide's most perplexing cold-case murder mysteries, after receiving a cryptic tip-off.

Detectives have told 9NEWS they have two letters, which link the shootings of model Corinna Marr and that of taxi driver Andrew Mordowicz.

Ms Marr, a 25-year-old model, was shot dead in her Collinswood unit in 1997. Her killer was never caught.

The author of the letter links the shooting of Ms Marr to another unsolved murder which happened 10 months earlier, just two kilometres away.

In the early hours of September 29 1996, Mr Mordowicz was shot dead, also with a handgun at close range, after being lured to an unoccupied home at Klemzig.

The killing was random, with any taxi driver able to respond to the call, including the victim's brother who was also working that night.

Police are investigating if the person who killed Ms Marr and Mr Mordowicz wrote the letters, which contain a series of riddles thought to be lines from a book.

"There are theories that the author is involved in both murders," Detective Sergeant Brian Swan said.

"However, there's other thoughts it could be just a person with some knowledge of both murders writing to police."

The hand-written letters were sent to police anonymously, but both were signed off with the same initials "T.O.E.".

The letters are now being forensically examined too see if new technologies can shed fresh light on the mysteries.