I see it the opposite; as officers of the court/Lawyers with legal training and knowledge, they should have made a report. We're not talking about 3rd hand knowledge of a "threat", we're talking about a "visibly upset" employee telling them of a solicitation to commit murder.
I have zero idea if LE would have acted or said thanks for the report. At least they would have done their part.
I've met many attorneys in my career I'd guesstimate 97% would have made the report, if for no other reason than to cya. The 3% I'd bet $ on not making the report, are the same 3% I'd expect to see doing interviews calling themselves whistle blowers. Not sure if they would have filed official reports, but at the minimum talked to an LE acquaintance with the information.
To be very clear the R's didn't kill anyone they didnt, solicit/conspire/ or as far as I'd guess add fuel to the fire. I still think they failed in their duties as decent human beings.
All my own opinion, which no one else is required to share.