The jury in the case also determined that Kim De Gelder could be held fully accountable in the killings, despite concerns about his mental condition.
There never was any serious doubt that De Gelder had killed the four victims, who also included a day care staff member and an elderly woman.
But the month-long trial centered on whether he suffered from a mental disease that affected his judgment when he committed the crimes.
The court said in a statement that the jurors found that there was "not the least bit of doubt" that De Gelder could be held accountable for his actions.
The trial was held some 50 kilometers (30 miles) west of the capital, Brussels, in Ghent, close to where the killings happened.