The attacks have a common theme of being carried out by people with a history of mental illness - but few of them have direct links to extremist groups, the officials say.Counterterrorism investigators globally are focused on plots by established violent groups with known ideologies, such as Islamic State, but on Saturday Munich police chief Hubertus Andrae said the Munich mall gunman, identified in news reports as Ali David Sonboly, 18, had undergone psychiatric treatment before the attack and was obsessed with mass killings.He had no criminal record and had no known connections to extremist groups.The German-Iranian, a local resident, shot and killed nine people near the Olympia shopping mall.The tactics in such attacks contrast sharply with those of the attackers in Paris in November, and Brussels in March, which were carried out by groups of militants with direct links to IS.Systems for collecting intelligence on extremists are not set up to identify individuals with a history of mental illness who come into contact with people or propaganda that could incite them to violence, the intelligence officials said.In the attack on a gay nightclub in Orlando last month, the perpetrator had viewed online jihadist propaganda, possibly produced by IS, the investigators said.But subsequent investigations turned up no evidence that the shooter, Omar Mateen, had any significant connections with IS or any other militant organisation.French investigators have arrested five alleged accomplices in the Bastille Day attacks in Nice but they have so far found no evidence that the attack was directed by foreign militants, according to US and French counterterrorism officers."When someone with mental health issues snaps, there is usually some external stimulus involved that provides an organising framework for the violent act," noted Paul Pillar, a former senior CIA analyst."Identifying those who might commit such acts and doing something to prevent them will always be very difficult."Self-radicalised individuals with a history of mental illness represent an entirely new variety of terror, said former CIA and National Security Agency director General Michael Hayden."This phenomenon allows truly troubled and truly dangerous alienated individuals to reach for a broader cause that gives meaning to their life." ..