That slots the Detroit plane bomber into a gruesome tradition: Islamist terrorists who trained as engineers.

There are plenty more. Khalid Sheikh Mohammed and Mohamed Atta, 9/11 mastermind and ringleader respectively: both engineers. Imam Samudra, plotter of the Bali nightclub bombings: an engineer. Kafeel Ahmed, who tried to bomb Glasgow Airport in 2007: an MPhil in aeronautical engineering from Belfast.

That link is more than coincidental. Analysing data on 284 jihadis from across the Muslim world, Diego Gambetta and Steffen Hertog found that 69% had been to university – which, if borne out , suggests al-Qaeda is better educated than the British workforce. And 44% went into engineering, with Islamic studies a distant second.
Put another way, engineers in Muslim countries were between three and four times more likely to become violent extremists than other graduates.

Why? It’s not just a case of being handy with explosives – sadly, terrorist bombs are relatively easy to make. And it isn’t simply because engineering is a very popular degree in developing countries – nearly 60% of graduate Islamic radicals in the west are also engineers.

The link has something to do with economics. A good student in Cairo, say, might expect to go on to a well-paid job – yet graduate employment across the Middle East is hard to find. Frustrated ambition is often a catalyst for radicalisation – just ask Jean-Paul Marat. But that wouldn’t explain why leftwing extremists tend to be trained lawyers instead.
Gambetta and Hertog point to a huge US survey in which nearly half of engineering students described themselves as both rightwing and religious – a higher proportion than any other faculty.

Being a God-fearing conservative means something different in Kansas than Karachi, of course, but even so, it’s a striking finding. And in a week when politicians are raising the old spectre of ethnic profiling, a little questioning must be a good thing.