Actually, you should be glad he was not prosecuted. By publicly not doing so, it gives the next honest gun owner a defence to fall back on - un-even application of the law has been held to be a factor in many convictions. Also, what evidence is there? He said it was a 30 round mag, but was it really? Maybe a legally blocked 10 rounder, maybe just a fake? A T.V. prop? Was it collected properly as evidence? If so, did it pass into others hands before being taken by police? Factors like above, that may have worked in his benefit, are there to work for all honest owners as well. Believe it or not, things like the letter of the law, rules of evidence, etc. are still held as being important to most courts and juries in this country... Bluster by the DC Police aside, I really doubt they could have successfully prosecuted him even if they wanted to, based on the newspaper facts of the case.
Larry