Police launch murder investigation over baby girl's death

South Australia Police have launched a murder investigation into the death of a baby girl on Saturday.

Nakita Jade Masling had been receiving high dependency care for almost 18 months in hospital after suffering a brain injury last year in Whyalla.

"She was 41 days old," Major Crime Inspector Greg Hutchins said.

"She's our most vulnerable citizen. She hadn't even commenced her life."

A man and a woman were previously charged with assault and criminal neglect but those charges were withdrawn due to a lack of evidence.

Anyone with information is encouraged to call Crime Stoppers 1800 333 000 or use the Crime Stoppers online reporting page.