Well yes, that was not good. But I really don't think you can judge a school by one horrible incident that happened off the school premises.
As long as a school has good teachers and a reasonable cohort of motivated children achieving good results (notwithstanding they will have their fair share of lower-achievers) then there's no reason why any child who goes there should not be able to achieve similarly. I know a boy who went to HG when it was very much a school to avoid, who got straight As and A* in his GCSEs, and he wasn't the only one.
Now they have some fantastic stuff going on, the music is amazing by all accounts. Yes, there will be some disaffectected kids from troubled backgrounds, but that doesn't make it a bad school. We're not in area for HG, but if we were I would definitely go and look - there's a lot to be said for a school with a mixed intake in terms of producing confident children with a good sense of their own strengths and weaknesses. Some of those schools are achieving amazing results with a very mixed bag of kids - although schools in more suburban areas may have better headline results, they are not having to work nearly so hard to get them, so on that analysis the inner-city schools may well be doing a much better job.
Take what other people say with a large pinch of salt - everybody has a vested interest in justifying the decisions they have made for their own dc, which may not necessarily have much basis in reality or any relation to the factors that are important in your own decision-making.
Go and have a look at all the various schools nearer the time, get a feel for what's going on there, and then weigh it all up.
