I’ve watched enough British mob films to be familiar with it as a term for snitching. I assumed it was from “snake in the grass” but there is a more complicated rhyming slang route from copper -> grasshopper -> grass shopper -> grass.

https://www.tripsavvy.com/meaning-of-grass-in-british-slang-1661909

The truth may never be known.

On top of it, the parents reassured the boys, in that final meeting, that the parents were completely innocent.

I believe that scene had a huge effect on what the sons did after, in terms of believing their parents’ innocence.

“Gassed up” was a typo on my part. The correct expression is “grassed up.”

Cue George Costanza. “It isn’t a lie, Jerry, if you believe it”. The Schneirs likely knew more minutiae about the case than any other party bar Milton / Radosh / Stern. They defended the Rosenbergs for 30+ years until that was simply unsustainable even for them. (Robert Nozick, having observed Walter Schneir at a public debate, adjudged the man a fanatic). It’s a reasonable inference that some of the red haze types the Meeropols interacted with were rather like that prominent figure that Richard John Neuhaus wrote about some years back, the man who told Fr. Neuhaus ca. 1975 that of course Alger Hiss was guilty but we couldn’t hand ‘them’ a victory by acknowledging it explicitly. However, others undoubtedly were perfectly sincere. To some extent, that’s the human condition and to some extent that’s how the portside is about everything (because they are overly invested in political disputes).

Tell the authorities.

The people who actually knew something 1st hand were Harry Gold, Morton Sobell, Alfred Sarant, Joel Barr, David Greenglass, Ruth Greenglass, and James Weinstein. The people who received confidential admissions from one of these are a fuzzier batch, but included the lawyers for the accused. Emmanual Bloch died in 1954; Marshall Perlin lived another 40-odd years, but he was inhibited in what he could tell them because his client (Sobell) was still alive (and the same stricture applied to Harry Gold’s lawyers). Harry Gold died in 1972; I’d wager neither of the Meeropol brothers crossed paths with him after 1951, if they ever met him at all. Alfred Sarant and Joel Barr lived the rest of their days in Soviet Russia; I’d wager neither brother ever met either man. The brothers quite self-consciously rejected what the Greenglasses had to say. Weinstein, a quondam Communist who was later editor of In These Times wasn’t involved in the conspiracy but was a witness to certain things, told what he knew to Radosh and Milton, told what he knew in public fora (e.g. the Townhall debate between Milton / Radosh / Stern and the Schneirs), and gave an interpretation of what he knew; he didn’t lie to them. You’re really talking about Sobell, here.