I was thinking about how this all happened in the week of Parshas Pinchus. Zimri wasn’t chayiv misa al pi din yet Pinchus was highly commended for taking action against him.
This murderer was transgressed on one of the three issurim of Harag val Yavor.
When Bais Din had to stone someone to death, like the Mikoshesh Eitzim, the Beis Haskila was far from the machana so that the person should have time to do teshuva on his way to death. Nevertheless Bais Din still had to kill him. We can’t make cheshbonos if he is doing teshuva or not- that is his department.
I think it would be a tremendous chillul Hashem if Yidden would come to the defense of someone who did something so awful.