The court also rejected calls by the families of victims for nearly 900,000 euros in damages. The families, who were seeking convictions in a civil suit against the officer, accused him of dereliction of duty and ten counts of aggravated manslaughter.
The officer had denied all charges.
The families have expressed their dissatisfaction with the verdict and may appeal against the court's decision.
The shooter opened fire at a college in Kauhajoki in September 2008. He killed nine students and a teacher before taking his own life.