If I have proposition to kill someone else for money, e.g. $10M, for exchange of 7 years in comfortable Dutch prison, I will grab the money.
In addition, convicts may be involuntarily committed when their sentence is over (and often before). This is aimed at rehabilitation, but can be extended indefinitely.
[1] https://nl.wikipedia.org/wiki/Lijst_van_tot_levenslang_veroo... (in Dutch)
How much people live in Dutch? If Russians will send one killer for every key men in country, country will be their in just 12 years, while they lose nothing, because Dutch prison is much much more comfortable than a flat in Rostov. I see that in Ukraine right now.