Reply To: lethal action in the times of the Gemorrah

Kanai’m Pog’in Bo for a forbidden relationship is only by a Bo’el Aramis (having relations with a non-Jew). And the Mishnah from Sanhedrin only applies to someone attempting to force a Na’ara Me’urasa and only applies before the act is committed. Once the act has begun you have to take him to Beis Din.