Ewilan wrote:

Good afternoon sherlockians,
Here's a season 4 theory I came up with recently, based on ideas I got from other series and what I'd like to happen (or not to happen). 
Basically, the last time I watched HLV, I noticed that as soon as Sherlock realized that there was no vault, he sort of disconnected from reality. He didn't say a word for about five minutes, and that is not just because of Mary's case, he wouldn't care that much about her. Some of you might disagree with this, but we're talking about a "high functionning sociopath", a man who committed a cold-blooded murder.

In my opinion, CAM knew something about Sherlock, something that could make his world fall apart (and we all know about this!) I'm talking about the CAM visit to Baker Street, where he mentions Redbeard. This is the proof that he knows things about Sherlock. He would not have remembered these if he could not use them to blackmail him afterwards, since that's what he does. 

Now here's the interesting part: we know that Sherlock has been doing drugs for a long time, and that Mycroft takes care of him when it's the case. We also know that there is/was another Holmes, and that we have not heard from him nor seen him in 3 seasons. Yet, Mycroft mentions him, and the fact that Sherlock is a murderer, in the same conversation. But what does "a murderer" mean, when this word is pronounced by a man who probably had people killed, because it is part of his job at the government? I believe that Sherlock had already killed somebody before (probably the third brother), and he is the only one to know about it. He covered the murder - which was easy for him - because Sherlock was high at the time, and hid it to Sherlock, who was so high he didn't remember anything about it. Though, he knew that something had happened (or else he wouldn't have killed Magnussen).

Finally, this crazy theory explains a scene from the season 4 trailer: Sherlock, in his MP, realizes that what he did. 
[img]http://www.cjoint.com/doc/16_07/FGAoPuZVDU5_Capture-d-écran-2016-07-26-16.40.27.png[/img]


What do you guys think about this crazy theory?

It's really interesting, no doubt. And it could be possible, yes. But personally I don't like so much dark Sherlock. His past definitely isn't white as the snow, but this is too much.
Sherlock didn't kill Magnussen for Mary, he did it for John. There wasn't need for more motivation.
But I agree, Magnussen knew about the third brother. Dead pet is hardly a big enough pressure point, so Redbeard is a code name for the the third brother or the the situation which leaded to the tragedy. There's possibility (more than possibility) that Sherlock blames himself for it and so dors Mycroft, but they don't speak about it, not directly, not openly. But i believe booth of the is putting too much of blabe on himself and the circumstancese were mostly out of their control.

 

I like this theory. Yes, it's quite possible that Sherlock has killed someone while he was high. I was thinking about that scene in TAB where Sherlock's frantically digging to find the body of E. Ricoletti and then a skeleton rose from the grave singing "do not forget me..." I thought it could be someone he accidently killed in the past.