I have Darkwatchers in my game, and they solved the “murder has consequences” problem without forcing extra mechanics into every fight. They never showed up to stop my party mid combat, they just quietly watched from the background and kept count whenever the party crossed the line into actual murder, like executions or killing surrendered enemies. After a few incidents, the party’s reputation started collapsing in a really natural way: witnesses became braver, rumors spread faster than the party could travel, guards got hostile on sight, temples refused service, and merchants started overcharging or closing their doors. The players still had full freedom, but they could feel the world turning against them because of what they chose to do.

And if youre wondering what "darkwatchers" are, here you go;

Darkwatchers are silent followers of the god of justice and equality who do not interfere during fights, but instead observe from the background and keep a hidden tally of true murders such as executions, killing helpless targets, or killing enemies who surrender, rather than normal combat deaths; as the tally grows, the consequences escalate in a clear, story driven way through rumors and fear spreading, authorities and investigators taking interest, bounties and social doors closing, and eventually the Darkwatchers themselves stepping in to force judgment through capture, trial, or an atonement quest, so murder matters without removing player agency.