Last reports state that the perp had been convicted of a an offence involving violence.
This is not a firearms ownership matter, this is a licensing matter. How did this person, with a violent crime record, manage to get a firearms license in this country with its insanely tight gun laws! But then, in Holland they’ve got thousands and thousands of illegal aliens living there, accessing welfare, health care, the right to vote (yes) and living the big life at the expense of Dutch taxpayers. So a firearms license doesn’t seem to be more than just a piece of paper with some bureaucrat’s stamp on it...
Update: 7 dead, not 6 .