There was a man in the United Kingdom recently, Raul Moat.
He was one of these people who had a bit of a dodgy background, nightclub bouncer and a history, and as such the police used to pester him and make his life difficult. This is kind of common in the UK. Then his ex girlfriend dated a policeman and bragged about it, knowing he hated the police, and generally to make him feel small.
He went and shot her, and the policeman, then knowing he was in trouble, shot another policeman and took out his eye. The result was quite a large undercurrent of support for him. Facebook tributes, messages, a shrine. The term "legend" was thrown around a lot. That policeman could never understand that while the majority of sympathy was for him, there was also sympathy for Moat, and eventually killed himself. The press were really nasty to anyone who sympathised with Moat, but the press were hated at this time for scandals, so that seemed to grow the support. It was as though people felt they were sticking it up to the establishment by supporting him. Lots of people blamed his ex girlfriend rather than him too. Around the same time, a man Derek Bird did a similar thing, but killing taxi drivers instead of cops. He was met with hatred and scorn. Yet people were fine with Moat killing police. I heard someone in a bar wishing he would take out a few more.
I think it's because people can relate. While the majority of police do a good job, it is true there is still an element of bullying, and there are still people drawn to that job because they want authority, and superiority over others. The story of someone like Moat resonates with the people who have had issues with the police and police harrassment (be they rightly or wrongly harrassed) and people identified with the fact that he seemed to be trying to turn his life around, but faced difficulties in doing so. While he was on the run I regularly heard people say "go on Moat" and from people you would not expect to take such an attitude too. Young intelligent students who had been pushed around by police while protesting government fees for example. It happened around the same time, and a large group of them really supported him.
Does it make what he did right? Of course not, he was completely wrong. Can I understand that certain people would gravitate to and identify with him? Yes. But this is really an indictment of society and morals as they are today. If you gave people reason to believe the police do a good job and are important, rather than the government's private army, and if people didn't see "them" and "us" and identified with the policeman as they do the taxi driver, then he would have been met with the same anger as Derek Bird was.
There has been a long standing decay of respect and trust, and that is down to the government and police to earn it back. People here are very anti-establishment right now, as we've been let down by our government, media and police. The press scandal, the banking crisis, the MP expenses scandal, immigration benefits culture, light sentences, student protests, London riots, police covering up the Hillsborough disaster, it's all happened within a few years. Therefore a rebel will earn some support, even when it is misplaced.
Every single one of us can emphasize with someone who has been pressured too much and finally "snaps". Where we differ is on how much of the "snap" we can justify and tolerate. For me, the moment someone takes another life, I lose any sympathy I may have had if they had killed themselves or sought help. But there are some that will tolerate and sympathise with them, no matter how they choose to vent their frustration.