Judge Edgard Altamirano ruled that Mairena was the mastermind of the murders of five policemen who died during a protest in a municipality in the south of the country and the kidnapping of two other officers. [Source]
Was he? You can't even begin to really lean one way or the other on it from the Reuters report. You'd have to go elsewhere to get any details whatsoever. Therefore, how is the report good journalism rather than pure false-propaganda?
The report says the violence was started by the government, but was it? Again, you can't tell from the report. The report simply wants you to take its word for it.
However, I've seen detailed reporting (highly credible, independent journalists on the ground in Nicaragua) on the subject that states the government did not start the violence but that fascists did. That reporting also states that the mainstream, corporate media knows the government didn't start the violence but that the fascists did and are covering up for those fascists. Also, actual history, the track record of the US in Central America, is on the side stating that the fascists started the violence.