Again, depending on what you mean by 'liberal democracy' and by 'killed their own citizens' then all developed countries (with the possible exception of Switzerland!) and a huger swathe of developing ones have done so, either by having the death penalty (still) in place or by starting/participating in wars.
I had a different sense of 'killed' in mind, Andrew. Most UK governments over the past 4 or 5 decades have had policies that effectively 'killed' jobs - sometimes intentionally, sometimes not. As a result, people's hopes and plans for their futures have been dashed and communities' futures destroyed.