The most striking aspect of the case is that it is explicitly not about truth. The Dutch ministry has written:
“It is irrelevant whether Wilder’s witnesses might prove Wilders’ observations to be correct, what’s relevant is that his observations are illegal...”
The illegality rests on whether his statements offend Muslims or incite violence against Muslims.
I've pasted the two laws Wilders is alleged to have broken below:
Article 137c Dutch Penal Code
1. He who publicly, verbally or in writing or image, deliberately expresses himself in an way insulting of a group of people because of their race, their religion or belief, or their hetero- or homosexual nature or their physical, mental, or intellectual disabilities, will be punished with a prison sentence of at the most one year or a fine of third category.
2. If the offence is committed by a person who makes it his profession or habit, or by two or more people in association, a prison sentence of at the most two years or a fine of fourth category will be imposed.
Article 137d Dutch Penal Code
1. He who publicly, verbally or in writing or in an image, incites hatred against or discrimination of people or violent behaviour against person or property of people because of their race, their religion or belief, their gender or hetero- or homosexual nature or their physical, mental, or intellectual disabilities, will be punished with a prison sentence of at the most one year or a fine of third category.
2. If the offence is committed by a person who makes it his profession or habit, or by two or more people in association, a prison sentence of at the most two years or a fine of fourth category will be imposed.