“It's very difficult to know if there is any link," between the four attacks which took place in Germany last year, terrorism and security expert Raffaello Pantucci tells The Local. "But it is quite common to get clusters of attacks following on from each other, and also to get ‘copycat' attacks."
In the USA, the FBI has been studying the phenomenon of copycat attacks with particular focus on shootings. A Mother Jones report revealed evidence that perpetrators use past attacks for inspiration, both in terms of logistical details and admiration for the media coverage generated - prompting calls for media to avoid reporting details which could 'glorify' the perpetrator.
"The incidents attract attention and that can attract other individuals who may already have these ideas - they get the sense that this is the right moment to act, and that doing something now gives their actions a greater meaning," said Pantucci, from the Royal United Services Institute (RUSI) in London.
But beyond the timing, the attacks had few similarities.
Each rampage involved a different weapon. An axe, a gun, a kebab knife, and a suicide bomb were used by the various attackers. And from the information currently available, the motives varied too.
The kebab knife attack on Sunday afternoon seems to have been due to a personal disagreement with the victim. Meanwhile, the gunman in Munich had a long-standing fascination with mass shootings, and photographs of Norwegian far-right terrorist Anders Breivik were found on his computer; the shooting took place exactly five years after Breivik killed 77 people.
"It is likely that he had chosen that specific date and had been planning the attack for a while, so it was unrelated to the train attack - which [itself] seems random, carried out by a troubled individual" says Pantucci. Although a handmade Isis flag was found at the Wurzburg attacker's home, there is no suggestion that he had had direct contact with or acted on orders from the group.
"The use of a bomb in Ansbach is more worrying because making a bomb is difficult, but there's no evidence that the attacker was linked to a particular group," says Pantucci. "It was likely to be a combination of his personal context [the attacker's asylum application had been rejected by Germany] and the general context of what's going on in Europe."
In fact, research carried out by German newspaper Bild has suggested that the bomb was not correctly made or detonated - implying that the bomber did not have the help of an expert bomb-maker.
Where a pattern does emerge is in the age of the perpetrators. The oldest, at 27, was the Ansbach suicide bomber. The others were 17, 18 and 21.
And the trend towards young attackers is wider than just those in Germany last week.
A report into terrorism in the EU, published by Europol last Wednesday, noted that, alongside an overall increase in terrorism-related arrests, there had been a particularly steep rise in young offenders. A quarter of those arrested on terrorism charges was aged under 25, compared to one in six two years ago.
Pantucci says this trend towards younger attacks is an "interesting detail", because lone actors are usually older. Adolescents and younger people may be more susceptible to outside influences, including, possibly, hearing about other attacks.
But, while four random attacks are certainly concerning for German authorities, Pantucci says the situation is potentially "less worrying" than what is occurring in France.
"The attacker in Nice, for example, had been planning the attack for a long time and there are lots of people he's been connected to, which suggests a much more dedicated jihadi figure.
"We've seen 'copycat' attacks in France, where it seems that the first attack had a clear jihadist link, but with the others it wasn't clear, and it's possible that they just get caught up."
Finding lone wolves
Hamburg's police force took to Facebook recently to urge the public to inform them of any worrying signs in friends' or family members' behaviour.
Authorities have difficulty recognizing those at risk of carrying out violence - particularly in the case of 'copycat' attackers who may be troubled but have no clear links to a specific radical ideology - but those close to them are often able to spot the warning signs, the post said.
Europol noted in its report that lone attackers are often unknown to police or security forces and are disproportionately likely to suffer from mental health issues, meaning that Islamist or other extreme ideologies can "have an aggravating effect" and may be used in an attempt to conceal individual or psychological motives.
"The overall threat is reinforced by the substantial numbers of returned foreign terrorist fighters that many [EU] Member States now have on their soil, and the significant rise in nationalist (xenophobic), racist and anti-Semitic sentiments across the EU, each resulting in acts of right-wing extremism," said Europol.
How to stop it?
After a series of coordinated attacks killed in Paris last year, German security forces feared a spate of ‘copycat' attacks in their country too.
"The attacks could work as a spark for people living or staying in Germany who are predisposed to such acts,” wrote the federal investigators (BKA) in an internal document at the time.
Pantucci cautions that we don't know whether this 'string' of attacks in Germany is over yet. But he believes German security are approaching it in the right way.
"The reaction in Germany has been reasonable and sensible. They've reacted very differently to France, where Hollande has 'declared war' and in the German context that seems to be the right thing," he says.
"The worst thing you can do is overreact by [making] mass arrests or declaring states of conflict. That can have a self-fulfilling prophecy; these groups are saying there's a war of the west against Islam, and if we refer to a war it breathes life into their narrative. In reality these are small organizations and they don't pose a massive threat. They can cause lots of misery and spread hate, but we can mitigate that by the right reaction."
"Germany is on high alert and they are a target for Isis, but overreacting on a political level would only exacerbate the high tensions around the refugee influx and the escalation of the far-right," adds Pantucci.