Of course. In time the state and its minions will become omniscient. Now stop resisting and get with the programme - be the first on your block with your very own barcode!
Firstly I have to ask you to accept the proposition that an arrest is a procedure and not, of itself, a punishment (although it seems like it at the time). In England and Wales there are "arrestable offences" and I'm sure unlawful killing (allegedly) is on the list. When the police arrest someone in England and Wales they are able to obtain evidence from the suspect and are able to conduct warrantless searches pursuant to the arrest. The police make the decision to arrest and then hand the case over to the Crown Prosecution Service which determines if there is sufficient admissible evidence for a prosecution. It would be very unusual, I would think, for police not to make an arrest in a killing. For the police to make a decision to exculpate someone involved in a killing is, I think, not aq good idea.
An arrest in such circumstances isn't automatic. In general terms, of course a UK police officer will only arrest someone having assessed the situation in the light of the law. Because of the significant differences in the laws of self defence in the UK and US though, an arrest here is bound to be more likely because, all else being equal, a crime having been committed is more likely. Again, arrest does appear to be used slightly differently in the UK and US though, and has (or should have) slightly different implications. I think it's wrong to assess this case as reported with an American mindset, just as it would be wrong to assess a case in the US with a British mindset. The fundamental principals are universal but the legal and social consequences individual.
Are you being facetious? the good ol'Mark of the Beast? I think everyone who wants one, should go and get one.......