Indeed. They're under pressure to find the perp. Look at the way the FBI has treated Hatfill.
Correction -- they're under pressure to find a non-Islamic perp.
I've actually got a fascinating take on this whole thing. I have no inside information, but after stringing a bunch of things together I've managed to come up with a very interesting scenario. I think I'll post it as a vanity tomorrow if nothing happens tonight . . .