The murders occurred in Gothenburg's Bergsjön district in January 2011, when two men aged 29 and 30 were found shot dead in an apartment.
An arrest warrant was issued on Monday for the 18-year-old suspect. He was also made an official suspect for complicity to murder.
Law enforcers took the teenager in on Tuesday morning and ordered a remand on Thursday. Remand negotiations were scheduled for Friday.
The 18-year-old, who was born in 1995 and lives in Västra Frölunda, was not previously known to the police and had not previously been considered a suspect in the double murder case.
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He could now potentially face charges of shooting the two men, who, after they had been reported missing for one week, were found dead in an apartment on Siriusgatan.