Even if he is trying to 'feel' something, this is a very scary manifestation of that. And saying it more than once is particularly concerning from a public safety standpoint.
If he joking, someone in his position of power (armed as he is) should NEVER joke about things of this nature.
And if he is mentally ill, he should not be in the position of power he is in, armed as he is.
And let's just say for the sake of giving him the benefit of MLC, that he is shaken up by the wedding, his losses etc and is in a really low place. For his 'way out' is to self-annihilate through harm to others is scary.
ETB, this is not a call for you to feel sympathy for H.
But as D reported it to you with concern, she may need your support to report his behavior. She will be learning in her studies at Uni (if she hasn't already) that she shouldn't normalize these sorts of behaviors. How can you help her right now?