He accepted evidence that was removed from re-assembly site?
OK
Yes, according to Sanders, several workers in the assembly building expressed concern over evidence tampering, etc and provided the seat foam samples.
While technically illegal, this could fall under "whistleblower" guidelines.
Sanders' sample was the only one tested and was found consistent with solid rocket residue. There does not seem be an explanation for why such residue might exist on the seat samples other than an impact with a missile.
Sanders provided another sample to CBS in an attempt to get a larger news organization involved. Unfortunately, CBS turned the samples over to the FBI without testing them.