It has emerged since the boy's mother had her stocking DNA tested on her own, because the police chose, despite the mother's appeals, not to do so, Swedish Radio Kronoberg reports.
The 17-year-old disappeared without a trace from a party in the middle of the night in early December - without either outerwear or shoes - and the case has received a lot of media attention.
A large search operation with dogs, drones, helicopters and volunteers started and it was in connection with that that the sock was found.
All attempts to find any other traces of the boy have, however, been in vain.
Several dives have also been made in the river Lagan without results.