That seems like a really high percentage of the dead were executed. Is it reasonably to guess from this fact that 2-6% of Roman mortality was caused by execution? That seems absurdly high. Maybe burial in a cemetery was more common for the executed than the otherwise deceased?
Related to that, there was recently a mock trial for a king in command of the army that won the battle where the archers annihilated the knights (edit: Agincourt). After the battle was over, he ordered his men to execute the survivors, under penalty of death if you refused. His men wanted to ransom the surviving nobles, who were worth a small fortune alive. But the survivors outnumbered them two to one, even after the battle, and the king wanted to take no chances. It was probably the correct decision, though he was found guilty in the mock trial.
But, not so much after executing some of them for ideological reasons. Their comrades quickly learned what the stakes were.
That wasn't/isn't typical for modern Western criminal justice; executed people tended to be buried in prison yards, often in unmarked graves.