The problem is modern societies have comprehensive records on such instances of murder, records that are systematic enough to be judged statistically. Not only were most murders not recorded (only special cases seemed to be noted in the histories), but most records of this sort did not survive the "dark ages." Copyists tended to prioritize religious or informational texts, not bureaucratic record ones. Meaning we have a lack of comprehensive systematic records on both ends, in the record, and the survival.

Also, here's the kind of lovely "record" of Roman crime that's an example of what has survived.

"The guilty thief is produced, is interrogated as he deserves; he is tortured, the torturer strikes, his breast is injured, he is hung up... he is beaten with sticks, he is flogged, he runs through the sequence of tortures, and he denies. He is to be punished; he is led to the sword. Then another is produced, innocent, who has a large patronage network with him; well-spoken men are present with him. This one has good fortune: he is absolved."

This is from an early fourth century Greek-Latin primer for children. But as you can see, what survives is intended for its "moral lesson" rather than any "neutral" record (this is presuming this incident happened at all, rather than being constructed).