The FBI has identified 21-year-old Dylann Roof as the suspect in the shooting in Charleston, South Carolina, after his uncle reportedly recognised him from the surveillance camera photo released by police.
A picture of Roof on his Facebook profile showed him wearing the Rhodesia (now Zimbabwe) and the South African apartheid flags pinned on his jacket.
Before firing on a Bible study group at the Emanuel African Methodist Episcopal Church, he allegedly said: "I have to do it. You rape our women. You're taking over our country. And you have to go". Shortly after news of the shooting broke, Charleston police chief Greg Mullen said he believed the attack was a hate crime.
Colin Roberts, who leads the research programme on counter-terrorism policing at Cardiff University's UPSI (Universities' Police Science Institute), told IBTimes UK the key question about the Charleston shooting is what catalysed the gunman to carry out the attack.
He said: "They may feel for example that what has happened previously completely justifies or vindicates their world view and they ought to do something. That they're going to make a stand.
"But until we know more about this individual, it's very hard to make any assumptions about it – for example did they have access to right-wing material, what was the motivation? It could be domestic. We don't' know.
"If he has been influenced by extreme far-right material – which is highly available in the US – the question is why now?"
Many people have been questioning why the shooting was considered a hate crime rather than a terrorist attack. Roberts admitted there is little difference between the two. He said: "Hate crime is what you might call a lower form, whereas terrorism has a design to impact as many people as possible within a community and they have a political motivation to do so. But hate crime and terrorist acts, often terrorist acts have hate as a motivation.
"If you look at Islamic State [Isis] propaganda, one of the simplifications that occurs within that is to simply all Muslims basically as the enemy. That simplification of the enemy happens in all hate speech. It becomes a very polarised, stigmatised, clear cut, simple objective. You see it all the time. It's a simple collective definition of people in society as the enemy or opponent."
Roberts was one of the authors into a report on hate crime in England and Wales in 2012. The paper looked at several aspects of the problem. Where, when and why do hate crimes occur? And who commits them.
Case of Lee Rigby
The researchers noted there are four categories for hate crime offenders: thrill seekers, area or territory defenders, retaliatory offenders and mission offenders.
Roberts said the murder of Lee Rigby highlighted several aspects of hate crime. Prior to his death, a Muslim man had been murdered. This could have served as a catalyst for Michael Adebolajo and Michael Adebowale.
Following the attack, right-wing groups looked to retaliate – there was an organised march by the EDL and the twittersphere was alive with messages of violence. One message said if people could not get down to Woolwich, south-east London, they should attack their nearest mosque.
As a mob mentality, this can lead to people committing acts of violence they would not have otherwise carried out. Roberts said: "There are thousands of examples of that behaviour. People don't know why they did it. That's very different from a highly motivated extremist."
Framing this to what has happened in the US, Roberts said there is a massive amount of encouragement for people who are on the verge of violence. He said: "With social media, the mob can be anywhere and they might never want to physically get involved in violence themselves.
"One very specific thing that's hard to explain. Its feature of serious ethnic violence – just prior to violence happening in social media and radio, etc, you get 'kill speech' emerging. That happened in Rwanda, it happened everywhere. Just preceding violence is this speech. In America this stuff has been going on for months now."
Roberts was keen to note the motivation behind the gunman's actions are unknown – it is not clear if it was racially motivated, religious our just that he wanted infamy. "Some want to do something where they will be remembered as a result of doing it – they want the notoriety," he said. "You see that at school-based killings... that they don't hate those people necessarily, they want to do something that vents their anger where they will be remembered forever for doing that.
"[But] we don't know who this person is or what their motivation is. We've got to be cautious that it is a hate crime at all."
Previous research has shown carrying out an act of violence on another person is very difficult – so the perpetrator normally has to be part of a group, as was seen following Rigby's murder, or a "highly motivated" individual.
Ferguson riots and racial tension
One of the indicators the attack could be racially motivated is the current climate in the US following the Ferguson riots after the shooting of Mike Brown. Roberts said conflict has been building for many months and these "retaliatory attacks" begin to emerge as a result of how people are being motivated. "They're getting angered by what's happening," he said.
Roberts pointed out that while there is not much research on the topic, it appears "an organised cloud of conflict builds around an atrocity". He said: "Here I'm not so sure. You've got this guy who pops up after Ferguson and other things that have been going for months. Then decides to kill loads of people."
Sometimes people who carry out hate crimes view social tensions as a cue that it is "the time engage" and that "it almost gives them permission to do it".
Over the coming weeks, much will be said about the gunman – who they are and what led them to carry out the crime. Roberts said the emphasis on this will be on the individual, rather than other ongoing social issues. He added: "It's part of American counter gun culture. They don't generally frame it around firearms being a problem, they tend to frame it around the individual being a problem."