The unidentified man captured and detained the boys, ages 14, 15, 16, in March, with the help of three other men. He then forced them into the basement of the store and tortured them for ten hours to force a confession of two previous break-ins, the Swedish news agency TT reported Monday.
One of the victims said the shopkeeper placed a wet towel over his face and poured water over his head.
The court called the actions "close to pure torture," the Swedish newspaper Mitti reported.
The shopkeeper was convicted on charges of kidnapping, aggravated coercion, robbery and abuse. An accomplice was sentenced to two years and four months, and another to community service. A psychiatric evaluation of the third accomplice is awaited before he can be sentenced, TT said.