"I am satisfied with the verdict. It is a tragic case with many cat owners affected and a young culprit who was very sick," prosecutor Madeleine Berndt Stragnér told news agency TT.
"This is the best verdict for him. He receives the care he needs while at the same time the risk of relapse is avoided," Berndt Stragnér added.
Between November 2011 and April 2013 eight cats were found killed in the west Gothenburg district of Högsbo. Another cat was also tortured but survived.
The events shocked locals, who organised a protest demanding stronger actions from the police.
According to the prosecutor, the boy strangled the cats and stabbed them in the stomach. A video clip was found in the boy's mobile phone and the police also confiscated a laser pointer, a multitool, four knives, a baton and gloves. The boy apparently used the laser pointer to attract the cats.
He was taken into juvenile care after admitting to the crimes. His mother and siblings were forced to move from their home after receiving murder threats.