Your source shows the rise in murder rates was well underway by the mid-1980s. It also fails to explain the recent decline. In 2007 there were 147 murders committed in the Netherlands¹. In a population of 18M, that works out to a rate of about 0.82 per 100,000. Looking at your chart, that is the lowest level since the early 1970s.
Your conclusion that lax drug laws are causal for a rise in murders is worthy of junk AGW climate science.
¹http://www.expatica.com/nl/articles/news/Record-low-murder-rate-once-again.html
Climate change research = Reefer Madness research
Both are govt funded with conclusions written in advance.