Who: Ibrahim al-Asiri AKA Abu Saleh – Saudi militant and chief bomb-maker for al-Qaida.
What he wants: To mastermind plots along multiple fronts, including renewed efforts to target Western aeroplanes.
What he does: The former chemistry student uses PETN in bombs – a white, odourless powder that X-ray machines struggle to pick up. He is thought to have designed the ‘underwear’ bomb used in an attempt to blow up a US-bound plane in 2009, and printer bombs sent from Yemen and destined for the US. His most significant threat, according to intelligence, is that he is teaching his techniques to al-Qaida apprentices, causing the ‘credible threat’ warnings issued by the US in July 2014 and led to increased security on all direct flights.
How he can be stopped: The US has intercepted al-Qaida transmissions and positioned him somewhere in the mountainous region of southern Yemen. More precise location intelligence will lead to drone strikes without fear of collateral damage.