Unconscious death wishes

In an interview, Peter Swales, one of the world's leading authorities - perhaps the leading authority - on the early life of Freud and on the early history of psychoanalysis (1), told the interviewer that, Freud had some fantasies about killing off his wife! (2) Interestingly, the interviewer didn't ask Swales to elaborate. So, how can we know that Swales was right about Freud's murderous urges regarding his wife?
Having access to Freud's letters to his fiancé, Martha, Freud's authorised biographer, Jones, learned, how mighty were the passions that animated Freud and how unlike he was in reality to the calm scientist he is often depicted.
Without a doubt, Freud was a violent person, much more so than usual. As Jones pointed out, He was beyond doubt someone whose instincts were far more powerful than those of the average man, but whose repressions were even more potent. (3) In other words, Freud only pretended to be a calm man of science, while covering his hatred of the people he interacted with. As he aged, Freud wasn't hiding his hatred of his fellow humans.

Monstrous longing

As it is apparent from his letters to Martha, Freud's emotions were not of the more usual loving kind. Thus, in one letter he confessed to her that he experienced, a frightful yearning - frightful is hardly the right word, better would be uncanny, monstrous, ghastly, gigantic; in short, an indescribable longing for you, (4) Without a doubt, Freud, already early on, in their relationship, displayed signs of emotional instability suited more for a murderer rather than for a romantic lover. Without a doubt, this isn't a confession of a sane person, but Martha was undeterred.

Freud's deadly anxiety

As Jones recounted, Freud was always very anxious about the health and safety of his precious betrothed. In the summer of 1885 there was news that she was not quite well.  Most people worry when a member of one's family is ill but, as it will be apparent, Freud's worry has a different cause.
Significantly, even though most people wouldn't realise what Freud was saying, and why, Freud wrote in the letter to his fiancé:
I really get quite beside myself when I am disturbed about you. I lose at once all sense of values, and at moments a frightful dread comes over me lest you fall ill. I am so wild that I can't write much more.
This is not a confession of a worried lover but of a madman that even Freud, to his credit, realised. As jones pointed out, already, 'The next day, on July 7, 1885, after getting a card from her he wrote: So I was quite wrong in imagining you to be ill. I was very crazy ... One is very crazy when one is in love.