It seems a jury of his peers convicted this shooter, based on the facts and the law. If the governor chooses to overturn that, it seems totally political and corrupt, in my opinion.
I completely disagree, but then I am intimately familiar with the criminal justice system...
A prosecutors discretion is near absolute. They have to consider their decision to prosecute based on the weight of the evidence, the reliability of witnesses, the criminal history of the defendent, the justifications likely presented by the defense, the severity of the crime, mitigating factors, aggravating factors, etc. Those are all legitimate considerations for prosecutorial discretion. Politics should not be a factor, but we all know that it is. I'm waiting with baited breath to see additional prosecutions in New York of nefarious criminals altering business records. My bet is on... not very many.
So it is that some prosecutors may choose to prosecute a crime to its fullest extent, when another prosecutor in a different jurisdiction believes that it would either be grossly unfair or the juice wouldn't be worth the squeeze. Since it's obvious that politics can play a role in prosecutorial discretion, there is almost always a system of special council or special prosecutor who is supposed to be independent of the elected official. That is to ensure that prosecutions aren't declined because of politics, when they probably should be prosecuted. The pardon is the other end of the spectrum. It ensures that convictions that were motivated by politics have some form of counterweight against them.
And yes, convictions come from a jury of your peers... but juries are limited to hearing evidence based on proper criminal procedure. The defense may be barred in many circumstances from stating that they were the only ones charged with altering business records in that jurisdiction in the past 5 years, and that would infer that they were on trial only because a prosecutor investigated the person and found an offense... when it's supposed to be the other way around.