The explosive devices detonated at two apartment buildings in Norrköping on the same day, November 23 last year.
The act is believed to have been carried out on behalf of the Foxtrot network, police have previously said, according to Norrköpings Tidningar.
No one was injured in the incidents. On the same day, another explosion was prevented in Norrköping after police seized a thermos bomb.
The longest sentence is for a 34-year-old man, who is sentenced to 14 years in prison. Three other people are sentenced to prison, while a 17-year-old boy is sentenced to closed youth care, reports P4 Östergötland.
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