[Rokurota]

The question should be where and when could we possibly get such a sample from Osama?

A previous sample from Osama would be ideal, but comparing his DNA (autosomal, Y chromosome and mitochondrial DNA) to known family members would be enough to give you good confidence.I understand we have DNA from some family members, including his son killed with him.

[Cyber Ninja]

I heard on the radio that the comparison is to a sister that died in Boston.

From the FDNY FAQ:

In the case of DNA samples the required tests may take several weeks to produce results.

This is where I'm skeptical.