There isn't much data before the late Middle Ages. There's virtually nothing systematic before the high Middle Ages: we have the law codes from the Early Middle Ages of course, but we all know that laws aren't always followed. Aside from that, we have some early medieval records of court cases, but they are only a tiny fraction of the records that have been lost, and the ones that were preserved were mostly ones that ruled in favor of the church and its officials (which was the reason these records were preserved). It's not till the high Middle Ages that you start to get more regular records from the most bureaucratic regimes (England, the Italian city-states, the papacy), but even then, the records remain too spotty and erratic to support general conclusions about rates. Even the late medieval records are few and far between (at least from a modern perspective), sadly.
You can certainly learn a lot about medieval practices and attitudes to violence from the records, but what remains of those records generally doesn't support the type of systematic, statistical analysis we would all like to see.