The 2nd conjecture is crap. If the Muslims ever did manage a nuclear detonation in our country the backlash would be felt world-wide. People of obvious Arab decent ( and yes you can pick most of them out, sadly some innocent non-Arabs would be targeted ) would be rounded up or neutralized by the armed civilian US population. In short any Muslim carrying a pacakage or driving a car would be summarily shot. As sad as that is, the US population would wake up to the fact we are at war and act accordingly that the fight was on our turf for the first time since 1865.
Your objection assumes that said terrorists would be wearing Islamic garb, sporting beards, and publicly bowing east for prayer. We just heard about Khalid Sheikh Muhammad's plans to employ southeast Asian Muslims for a follow-up to 9/11. So, who exactly will we be profiling? Anyone who isn't white? So they'll use Chechen/Baltic types.
Anyone carrying a suitcase nuke would assumedly vaporize with everything else, anyhow, so we probably wouldn't even know the ethnicity of said nuclear bomber.