It didn't take long. Within days of the Brussels murders, the conspiracy theorists (for which, read: "the Jews did it") were at it. Step forward, Tariq Ramadan, lecturer on contemporary Islamic issues at Oxford University and Muslim Brotherhood aristocrat - the grandson of Hassan al Banna, the Islamist group's founder.
Supposedly a moderate (although it takes a three-second Google search to puncture that idea), Ramadan wrote that Belgian officials seemed to be part of a conspiracy to present the Jewish museum murders as antisemitic when they were no such thing, because the victims were Mossad agents and the killings were a professional hit job. (Ignore the fact that two non-Israeli Jews were also murdered. If the facts don't fit a conspiracy, best just ignore them.)
"The two tourists targeted in Brussels worked for the Israeli secret services. The government does not comment," Ramadan wrote. "Coincidence. Is this a case of anti-Semitism or a manoeuvre to divert attention from the real motives of the executioners? We oppose all slaying of innocents and racism but at the same time, it's time they stopped taking us for fools."
I'd never suggest that anyone takes Ramadan for a fool. A knave, on the other hand... Because almost immediately after Ramadan deployed that familiar Jewish conspiracy trope came the news that the French authorities had arrested Mehdi Nemmouche, an Islamist terrorist brought to the boil in Syria.
Not, of course, that anyone could have expected a lecturer on contemporary Islamic issues to have any idea that there might be a possibility that a man who shoots Jews in daylight in the middle of Europe could possibly be an Islamist terrorist. Of course not.
A British intelligence chief said: 'Belgium is top of our concerns'
Indeed, most likely this will be the first instance of a Syria-trained terrorist operating on the streets of Europe, rather than the last. Almost half-a-million Moroccans live in Belgium. Hundreds, if not thousands, have fought in Syria. And when they return to Belgium, all they need is their EU passport to operate anywhere.
As one British intelligence chief put it this week: "Belgium is top of our list of concerns. It has a large proportion of radicalised ex-fighters of Moroccan origin. All of them are just a Eurostar journey away from London."
What makes this doubly difficult is that the Belgian government has for years had a "hear no evil, see no evil" attitude to Islamists. The Belgian view is that if they leave Islamist groups alone then they will leave Belgium alone. It's a typically cynical, morally corrupt view from a country I came to regard as itself cynical and morally corrupt while I worked in Brussels.
The British authorities are criticised for refusing to take Islamist hate speakers seriously but compared to the Belgians, who give these groups near-free rein to spread their poison, we are models of good practice.
The Belgian poison is developed from a mix, unique in Europe, of open Islamism and open antisemitism.
A few months into my time in Brussels, I walked into a restaurant a friend, who looks Jewish. The waiter (who apparently didn't think I also did) asked what "the Jew girl" wanted. When we got up, saying both Jews would leave, he replied they'd only have served one Jew, anyway, not two.
Last year, Joods Actueel published a survey of 4,000 Belgian children aged 14-18, which found about 75 per cent of young Muslims agreed with hard-core antisemitic statements such as that Jews want to dominate, have too much power and consider themselves superior to others. Only 10 per cent of non-Muslim children agreed.
And now the rest of Europe is suffering the consequences.