How do you identify the seller in a large block trade?

[3259]

Per Seeking Alpha, a large block trade played a role in ATUS trading down today. End of day, it was down 4%. The trade was for 13.8 million shares, which is more than Blackrock's holding in the stock and almost as much as Vanguard owns. This raises questions like:

 

1. who is selling this much stock?
2. why are they selling?
3. what do they know that I don't?

 

Is there a legal and efficient way for a retail investor to find out who sold? Only thing I can think of is looking through shareholder lists and trying to guess or waiting weeks (months?) for SEC filings to come out. How does Seeking Alpha know about the trade, the bank involved, and how many shares were involved? If they know all that, why aren't they reporting who the seller is?

 

Here's the article I'm talking about:

 

https://seekingalpha.com/news/3733342-altice-usa-stock-dips-3-on-report-of-138-million-share-block-trade

[Gregmal]

Find a Jewish housewife type prime broker. Otherwise, next to impossible. 

[maplevalue]

In Canada you can see the volume, buying bank, and selling bank for trades on the TSX (e.g. https://money.tmx.com/en/quote/FFH/trade-history). I believe the US is similar. In terms of the clients behind the trade the only people that would know that are the sales-traders at the investment banks that did the trade (possibly these people won't even know).