To me, the title chosen should be the one most recognisable in a Google search. While Woolwich murder and Woolwich attack are both currently common in sources, I don't see how 'murder' helps anyone not familiar with the incident to recognise it. There were 99 murders in London last year, some of which either deserve or already have Wikipedia articles I would have thought. I doubt there's any that are about attacks in Woolwich in 2013. Bearing in mind that on Wikipedia, calling something an attack in a non-warzone in these times, basically means terrorism, and more often than not, will involve murder. To illustrate that - London attack is already a redirect to List of terrorist incidents in London which obviously has a link to this article, whereas London murder goes nowhere, and gives all sorts of random articles in the search results, none of which appear to be of any use to someone looking for this article. Similarly, Woolwich attack already redirects here, whereas Woolwich murder goes nowhere (although I'd have no objection to it coming here).