The explosions took place in January, next to two apartment buildings in the Gideonsberg and Öster Mälarstrand areas.
The 29-year-old, who has been convicted of, among other things, preparation for public destruction and aggravated weapons offences, is suspected of having made the bombs in Katrineholm and then transported them to Västerås.
A 16-year-old boy is sentenced to ten months in a closed juvenile facility for planting one of the bombs. An 18-year-old man is sentenced to four years in prison for instigating the second explosion, when he forced a minor boy to carry out the crime.
No one was injured in the explosions.
