Whoever he really is, it seems he was a white hat.
Here’s my guess - the mysterious guy infiltrated antifa as an undercover agent and entered the Capital with them. He could have taken evidence away, including laptop(s). Antifa doxxed him but that would be his ‘cover identity’ (bartender) and not his real one. He won’t be found.
Either that, or I watched too many spy series when I was growing up!