I didn't say that law enforcement was involved in a cover up. Why would the Bush administration give an investigatory task to a non-investigative agency like FEMA? (the same agency that fouled the response to Katrina).  The biggest crime in US history and the FBI and BATF were not involved?  The only people who can rule out the use of explosives are law enforcement investigators who have done a presumptive test for the presence of explosive residue, not volunteers sifting through rubble.