This time last year, I was in Brussels, flying back at the end of my first trip to the Belgian capital from the airport at Zaventem which on Tuesday morning was the scene of two of the three bomb attacks which struck the city.
As I suppose is natural, it's more shocking when a bomb blows up somewhere you've been to or know well, with the inevitable thought of "there but for the grace of God go I". I must admit that, even after I'd been to Brussels, I wasn't really aware that it had a sizeable population of North African Muslim immigrants or that its Molenbeek district was home to large numbers of jihadis who had returned from fighting in Syria: like most people who go to Brussels, I stuck to the the tourist quarter around the Grand Place with its bars and cafes.
After a massacre such as this week's, the inevitable question is asked: what we can do to stop it happening again? Last night, in a special edition of the BBC's Panorama programme, the investigative journalist Peter Taylor sought some of the answers.
For the the last decade or so, Taylor has been investigating the role of the intelligence agencies in the fight against Islamist terrorism (before that, he spent much of his career looking into their covert operations in the thirty-year conflict in Northern Ireland). A few things soon become apparent about those suspected of carrying out the Brussels attacks and the ones in Paris last November: they tend to have friendship or family links with others in their terrorist cell, to be from not particularly religious backgrounds, to be involved in petty crime and are often recruited whilst in prison.
If the alienation felt by many young Muslim men in Europe, which leads some of them to become jihadis, has socioeconomic rather than religious roots (albeit that it often take a religious form), the answer to the violence perpetrated on the streets of its cities becomes clear: tackling the lack of integration in housing and schools and providing decent jobs as an alternative to the low-level gangsterism which sees some of them eventually enter the ranks of Islamist terrorist networks like ISIS. The real question is whether European governments have the desire to do it.