From before it was handed down:
That was the case here. But it does not follow that the marine will get a 30-year minimum. Parliament would presumably have had in mind the use of a firearm that was unlawfully held or, at the very least, a firearm that was not meant to be used for killing people. On the other hand, those who are trained to use firearms in self-defence police officers and troops have special responsibilities not to use their weapons unlawfully.
Cases that do not fit into the 30-year category have a starting point of 15 years. But once the court has chosen a starting point it must take into account any aggravating or mitigating factors.
...
In the end, it may not make very much difference whether the court starts with a 30-year tariff and works down or begins with a 15-year tariff and works up. Blackman's use of a firearm is clearly an aggravating factor even though it appears in the part of the schedule dealing with starting points.
All this suggests a minimum term higher than 15 years but not nearly as high as 30 years. My guess would be around 20 years or a little less.
http://www.theguardian.com/uk-news/2013/dec/05/marine-life-sentence-sergeant-blackman-murdering-taliban-prisoner
I suspect Rozenberg was thinking too much about a murder in the UK; they may have decided a firearm is actually not 'aggravating' inside Afghanistan, since soldiers and others carry them openly all the time, and the victim himself had, I presume, been habitually armed.