It was in May last year that a woman and her son were found with extensive injuries in connection with a villa in Mälarhöjden in southern Stockholm.
Both died the same day from their injuries.
The six-year-old boy's siblings managed to escape to a neighbor who was able to alert the police.
The sibling could also say that the perpetrator was a relative of the family.
Now the relative, a 41-year-old man, is sentenced to forensic psychiatric care with a special discharge examination.
The man is from Uppsala and has previously been sentenced to forensic psychiatric care, for, among other things, assault.
SVT is looking for prosecutor Ingrid Viklund