They need something unmistakable and horrifying...worse than 911. It has to be concentrated and instant, to make for the excellent photo op and sound bite. It has to be something the entire Islamic world (much illiteracy in some of those third world countries) can recognize as being the handiwork of OBL against the "Great Satan." In other words, it has to be extremely violent.
Two stories in today's news cycle mentioning money going OUT of U.S. . . the Syrian woman nabbed at an airport with $24K on her person and the North Carolina video taper who had just wired $100K home to Pakistan(?) . . . anyway, the outflow of funds suggests that the planning phase is over and the operation itself is upon us . . . let's keep our eyes open for any other stories that mention terrorist funds going out of the U.S. . . if really a trend, then it's trouble . . .
A preliminary bio attack would leave the goblins free to do other things. If they attack us violently first, there may not be an opportunity for them to do anything else. They couldn't look out of a window without taking a chance.
This does require that they have bio here, and in quantity to deploy enough to compensate for the low efficiency. We know that they're coordinated.
Agreed - I tend toward truck/limo/tanker bombs - almost impossible to defend against - economical and massive impact potential.