When the home care service arrived for a planned visit to the couple's shared home on September 9 last year, the man said he had killed his partner, prosecutor Anders Stridh says.
The woman was found with serious knife injuries and taken by ambulance to hospital, where she was pronounced dead.
There are no previous reports or convictions against the man.
"There were early signs of a mental health problem," the prosecutor says.
According to the forensic psychiatric examination, the man suffered from a mental disorder at the time of the killing. He does not deny using a knife against the woman, but denies responsibility for the crime.
