Wikipedia map of homocide rates and see that Poland has one of the lowest rates
The number of homicides has risen to 519 in the year 2017, an increase of 50 in relation to the previous rate - acording to the
Rzeczpospolita daily. So according to your data, the number in 2016 was
256, but according to my source, the number was
469.
A big difference! Here are numbers for the years (liczba zabójstw w Polsce; source: Komenda Główna Policji):
2014 - 532
2015 - 502
2016 - 469
2017 - 519