The knife attack on a train in Austria in which two people have been badly injured follows the attack on a Swiss train in which two people died.
These are tragic episodes, almost certainly carried out by people who are mentally ill.
The full details and context of the attacks will become known in the coming days but there have been similar attacks in Britain and across Europe by troubled people.
It is important to emphasise that the overwhelming majority of people who suffer the agony of mental illness are of no risk to anyone but themselves, and suffer with fortitude and without complaint. However, the craze of Islamic extremism has given a regrettable violent motivation to a tiny number of people who are severely unwell.
And the people who carry out atrocities such as Nice or Orlando are deeply disturbed, even if they are not suffering from a recognised and diagnosable illness.
It will always be impossible to prevent all such attacks, unless we stop the manufacture of knives and blunt kitchen utensils and ban the use of vehicles.
The current spate of terror needs a two-pronged response.
A society-wide awareness and denunciation of the disgusting concept of jihad and utter abhorrence of anyone who advocates such murderous violence, however obliquely.
This is a nation where we cherish free speech and freedoms generally and democracy and tolerance. But we must not shy away from pointing out that there is a fanatical Islamic core that does not share those values.
People who leave the UK and abuse their citizenship and the privileges that it brings to fight murderous jihad abroad must be given the most severe sentences on their return.
Meanwhile, funding for mental health services to improve the lives of some of the most vulnerable people in society must remain a top priority for public spending. Stormont spends millions on free prescriptions and inefficient hospital provision that could be better spent elsewhere in the NHS.