After serving his sentence, the 18 year old will be deported from Sweden and banned from ever returning.
Kalmar district court awarded Abbas Rezai's mother 113,000 kronor in compensation.
In its judgement, the court wrote that the crime for which the 18 year old was found guilty was deserving of life imprisonment. But the sentence of four years' secure youth detention was due to the fact that he was only 17 when the crime was committed.
The verdict was not unanimous. Two of the judges in the trial said they believed that the 18 year old's mother and father were also guilty of murder. They wrote that who had done what was certainly not clear, but that it was beyond any doubt that the three on trial had planned the killing together.
Abbas Rezai was found dead in the apartment belonging to the Afghan family in Högsby, in Småland. According to the prosecutor, Kjell Yngvesson, the murder was an honour killing, in revenge for Rezai's relationship with the 16 year old daughter in the family.
The mother, father and son were all tried for murder, but from the beginning the son claimed responsibility for the crime. He stated that he and Rezai had had an argument which had escalated into the violent killing.
Abbas Rezai had been beaten with an iron rod and a baseball bat, and hot oil had been poured over him. He was also stabbed 23 times with a 29 centimetre knife.
The prosecutor maintained that both the parents and other members of the family had collaborated in the murder. He demanded a life sentence for the parents and a long jail sentence for the son.
The first to comment on the judgement was Karl Olof Wirell, the defence lawyer for the 40 year old mother in the family.
"It went exactly as we thought," he told TT.
The 18 year old's lawyer, Helena Karlsson, said to TT that she was satisfied that the court had believed her client's story, and described the murder as the result of a fight between two young men with catastrophic consequences.
"It's a success for the defence that the court found my client not guilty of the charge that he had been involved in planning an honour killing and that he had lured the 20 year old to Högsby to kill him," she said.
She accepted the punishment, but expressed disappointment at the decision to deport the 18 year old after his sentence.
"He was just 15 when he came to Sweden and he has his family here," she said.
Helena Karlsson added that she would discuss a possible appeal with her client.