So if I am to draw all the threads together, the theory is that the person who has been arrested for both the murder of AW and for unspecified potential terrorism related matters was somehow radicalised, influenced or inspired by an online organisation or group. And targeted AW because of one or more of her expressed socially conservative views (like Charlie Kirk in the USA).
With the link to HH is that HH appeared to know that Ann’s death was due to violent means and not a natural death before the police made that public. Which HH may have known through sharing of information on the web/devices if HH also frequented the same online places and chats as the arrested suspect, hence the checking of HHs hard drive.
I mean it’s not too much of a stretch. Of course HH could just be an individual who expresses unpleasant views on a regular basis and in the case of AW it is entirely coincidental and bad luck for HH that her death turned out to be murder.