Religion aside, adultery is not acceptable, and I could understand a religion punishing for such, but I wouldn't say it's deserving of capital punishment.
This idea God was cleansing via suicide - well, it's so ignorant and stupid. The Nazi anology has strength, but then the USA does kill murderers, which is a form of cleansing by death.
I find it crazy how so many things are attributed to holy spirit, or Jehovah's direction, when it blatantly wasn't. Even if Jehovah decided capital punishment was the answer, the young brother chose to jump in front of the train - how can these people imagine holy spirit directed things? It didn't make the train derail and fall on the young man! There was no spirit involved.
Presuming this young man really believed in Jehovah, didn't go to Bethel for his parents, he was probably so overwhelmed with guilt he had been taught to feel, so fearful of Jehovah, that he commited the sin of suicide, ignoring the sanctity of life - this is crazy - guilt for sin drives to more sin.
People could say that it he was thrown out Bethel for not following the rules - doctors are struck off for ignoring rules, such as recreational drugs, as are lawyers. It could be said that people can't just expect their family to be there and take them in (many people have family problems or family overseas). But it cannot be denied that lawyer, brother or doctor, this would be emotionally difficult and all be left in a such a difficult financial situation.
Probably pioneered from school, did some cleaning work for another brother, then went to Bethel, so has no qualifications, little work experience recognised by the world, and had trouble finding work/home. Not to mention how naive and isolated growing up in the Truth makes one to worldly life; it's hard not knowing how the world works. On top of this, his whole life is shattered, career destroyed, God rejected by him, disliked by family. He doesn't have any friend to turn to as they ignored him for being disfellowshipped. Therapists don't care. I expect this guy couldn't cope.