The attack took place after the two boys arrived in Rödeby, a small town near Karlskrona, on a moped. According to police, the boys got into an argument with the 50-year-old, who is then thought to have produced a shotgun.
The authorities were alerted after residents heard shots being fired. The 15-year-old was found dead, while his 16-year-old friend was taken to Karlskrona Hospital to be treated for his injuries.
The 50-year-old was arrested shortly afterwards on suspicion of murder and attempted murder.