The only thing I can ever think of is to know thy neighbour. The only way to prevent these kind of horrors from taking place is to know people in the neighbourhood, to recognize signs. I don't know about exact cases, and I certainly haven't been around as long as most of you guys, but I think it's safe to say that over the years direct contact has become less frequent and in general contact with strangers (in shops, public transport etc.) has become colder. That is something we can work against, and something I'd hope lessens the chances of cases like these going unnoticed.