New Delhi, May 29: The recent terrorist attacks in Riyadh and Casablanca seem to have emboldened al Qaeda which has heightened its recruitment drive and is "trying to develop explosives" which are harder to detect while boarding an aircraft, according to intelligence reports quoted by Pakistani media. Quoting US counter-terrorism experts, daily 'Dawn' said al Qaeda was "trying to develop explosives which are harder to detect, to be placed in shoes or luggage, and would be used to blow up a passenger aircraft. "It is unlikely, the officials said, that a terrorist team would follow the example of the September 11 hijackers spending months in the us before a new attack. More probably, they would remain abroad until they choose the time to strike." Among the recent major arrest of al Qaeda activists included that of Tawfiq bin al-Attash, who was the mastermind of the 2000 bombing of American warship USS Cole. The raids in which al-Attash was caught also led to the capture of truckloads of explosives, which led the agencies in Pakistan to express surprise as to how could such a large amount of bomb-making materials be smuggled into the country. Bureau Report