Rav Moshe wrote in the same teshuva “there were almost no Jewish murderers because of the awareness of the severity of the prohibition of murder and because they were educated by means of the Torah and the punishments of the Torah to understand the seriousness of the crime.”
The translation — and it IS faithful to the Hebrew — was done by Rav Daniel Eidensohn, author of the Yad Moshe index to the Igros Moshe. My apologies for that omission.