So ... my client posted a violent fantasy about me!

I'd play merry hell about this.
Tell HR. Show and tell the client. Tell his seniors. Post it on Twitter. Rent one of those cars with a megaphone on the roof. Spend the afternoon in a sign writing plane. Let him know you KNOW.

You never need deal with this scumbag again. I wouldn't, and I'd let the world know why.

Maybe don't see it as demanding rectification, but as avoiding future contact.

"After his meeting with Eleanor, your Junior Staffer posted this violent fantasy about Ellie. I'm afraid my company will not agree to any more contact with Junior Staffer; none of us feel safe dealing with him now that we know what's going on behind the mask. We will be happy to continue dealing with your company if you would like to appoint a different contact person."

Of course only do this if you're genuinely prepared for them to choose not to buy from you any more.

do the police ever keep witnessess confidential - so if OPs friend was to confirm she knew it was from him, would that help it be recorded and could she remain anonymous?

At my work we do training videos about scenarios where clients are offensive/abusive, and the message is to report it. Your company has a duty to protect you from abusive interactions, regardless of how senior you are. The suggestion above to take this up with client firm’s HR to investigate sounds the best approach to me. They won’t want their firm degraded in reputation by such behaviour.

This is the Met, but will be the same for anywhere:

https://www.met.police.uk/advice/advice-and-information/har/harassment-on-social-media/

'If there has only been a single communication, it’s unlikely it would qualify as harassment, but could be considered a malicious communication. For such an offence to be committed, a message must be sent to another person, or sent via a public communications network, that is indecent, grossly offensive, obscene, threatening or menacing.
How to report online harassment, malicious messaging or distribution of private sexual images without consent

You can report harassment, malicious messaging or distribution of private sexual images without consent online or by calling us on 101.

We will be able to confirm whether an offence has been committed, based on the full facts and your individual situation. In order to assist us with our investigation you must not respond to the message as it may encourage the sender and make the situation worse.

If possible, take a screenshot of the message so if it gets deleted later there will still be a record of what was said.'

Does it have his name on it? If so an anonymous email to his HR and manager could be sent.

In light of the recent Russell Brand controversy they should be pretty hot on cracking down on creepy behaviour.

certainly don’t meet one on one with him ever going forward.

I would love to be proved wrong! It's horrible for the OP.

That is so scary. You should insist you're not going to work with him.

yes I agree, I think any matter of recording is necessary. I imagine an ideal situation would be for you never to work with him again, and also for him to know that it has been legally recorded

This is horrible, OP. I'm so sorry.

I'm not quite so sure that police would be disinterested - I know of a [slightly] similar situation that the police took very seriously as a credible threat and issued a warning. I think if nothing else recording it is worth your while - keep any and all evidence.

Has it been posted publicly? How did the person who sent it to you come across it?

Not as far as I know - no crime number is issued.

In the OP's case, IANAL, but I cannot see what offence has been committed. It is sadly not unlawful to describe your violent fantasies about women online - it if were, half of the internet would be closed down. If the creep had sent the post to the OP, it might be different, but he hasn't

What if the lines between the truth and fantasy are merged for x.

How would you know you are safe? Is it a risk worth taking?

I think as a last resort, at the very minimum, if you have a 1 - 1 with this strange character you need someone with you not just for protection but as a witness.

Ok, so as a woman who has been a senior manager and with client responsibilities this is what I would do. Contacts the head of HR at his firm, not yours. Explain that it looks to outsiders that their relatively junior employee is posting this crap about you, a business partner. You expect them to investigate and confirm to you that either it wasn’t him, or it was and they have reassigned him, preferably to the unemployment line.

do they record it?

i think also, regardless of whether he did or didnt make the fantasy, you need to report it to someone in work. The whole thing is weird, even if his colleague is wrong, to be sent that by staff of their company implying that it is about you. How could you continue to work with them.

OP, what advice are you seeking from us? on how to deal with this in work, or general safety advice?

Sadly, I doubt the police will be interested. The creepy shit has not actually made any threats to the OP, or shared the post with her himself, to suggest an indirect threat.

We deal with scenarios like this a fair bit at my work (medical) and the police usually cannot help unless there is a direct threat.

Contact first your line management, suggesting a plan to contact his. Show them the 'story' pointing out similarities in his writing plus any real life events (dates and times) and stressing that whatever happens, you no longer wish to have contact with this man.

Depends on content but could it be of interest to the police? He's clearly identifiable, you are identifiable and it describes violent intent.

If your HR are professionally qualified, they have professional responsibilities. So even if the HR person is very junior to you, they will have resources to consult and standards to uphold. I would go to them and ask them to take professional advice about what both they and you should do.

Sorry to hear this. It's absolutely terrible. Fucking men.

I would definitely ask his colleague how she knows - if there is anything that makes it certain I would report it to the police. I would then inform his work you have reported it to the police.

Since you are the account manager and he is replaceable, do this.

Speak to your line management first.