do you understand the geography of the area he did it in, the way he moved around the area and the speed at which he did it? The police were very close to him but the nature of how shootings were reported (as people were found, not as they happened) meant they were chasing shadows. In that area there are normally tens of ways to get to the same place via various C road (i.e. single car width normally) and an experienced taxi driver would have a distinct advantage.
I was in one of the neighbouring villages at the time, the frightening thing was that you didn't know which town he'd pop up in next.
Both his weapons were legal, he was never deemed a risk and no-one suspected he would do it. You can legislate all you like but you'll never legislate against the completely unexpected or unimaginable in my opinion.