Police have opened a double murder investigation into the mysterious deaths of an elderly South Australian couple almost a year apart.

SA Police said Brenda Anderson died in an Adelaide hospital on March 16 last year, while her husband died on May 1 this year, after being found unconscious at home.

Detective Inspector Mark McEachern said similarities and abnormalities in the toxicology results from husband and wife had raised suspicions they were murdered by the same person.

Mrs Anderson died at Flinders Medical Centre, in Adelaide’s south, after being transferred there from Noarlunga Hospital on March 12, 2022.

“Mrs Anderson’s hospital death was identified during the coronial investigation process after toxicology results gave significant rise for concern,” Detective Inspector McEachern said on Thursday.

“When an innocent explanation for toxicology abnormalities was eliminated, the possibility of Mrs Anderson’s death being a deliberate act by another party became the primary subject of the investigation.

“It is believed Mrs Anderson was killed by a person known to her and in close enough relationship to have been visiting her while she was in hospital.

“Police have no concerns about the level of care in either hospital, which was exemplary,”

Meanwhile, Mr Anderson was discovered by a carer, unconscious at his home in the outer southern suburb of Hackham on April 30 this year.

He was taken by ambulance to the Flinders Medical Centre and died the following day.

SA Police said suspicions about Mr Anderson’s toxicology results had led to concerns about the circumstances surrounding his death.

“Police have eliminated external carers involved with Mr Anderson‘s care as being involved in his death. We have identified a suspect and won’t elaborate further,” Detective Inspector McEachern said.

Police are appealing to anyone who might have had contact with Mr and Mrs Anderson and might have knowledge of their deaths and the circumstances that led to them.

They are particularly keen to speak to anyone who knew what prescribed or non-prescribed medications the husband and wife were taking or had spoken about.

Anyone with information is asked to call Crime Stoppers on 1800 333 000.