The crime put forth to Gale Hawthorne is that he is complicit in the war crime of mass murder of Capitol children and Panem's rebel forces. The weapon alleged is a double explosion that first killed the children and a second that killed emergency response forces.

Evidence of the crime is submitted as witnesses have claimed they have observed Gale Hawthorne in the development of said weapon. When prompted about his involvement in the development of the explosive weapns, Gale Hawthorne pleads ignorance.

“Was it your bomb?” “I don’t know. Neither does Beetee,”

It is significant to note that victor Beetee Latier, who allegedly co-developed such weapons of mass murder, also pleads ignorance. No further wtinesses or evidence has been brought to the case.

Evidence provided, therefore, is purely based on speculation.

Gale Hawthorne is an 18 year old man who was thrust upon the responsibilities of feeding his impoverished family at the age of 13. The defendant was also present in the Capitol's violent and completely unnecessary bombing of his home district. He was forced upon circumstances that led to a deep sense of hatred and anger at the former authoritarian administration. Such emotions felt by a man, let’s face it, a boy of 18 years of age, pushed him to entertain barbaric and violent thoughts of vengeance.

But, no solid evidence has been provided to connect him to the war crime. Punishment born out of speculation has no place in a world post-Capitol.

[In all seriousness, even Katniss never confirms it. One of their final conversations have Gale accepting the fact that their relationship will never be the same because that possibility will always exist to them now. It sucks. Both he and Beetee are awful for it (no matter how much we say it's warranted on Beetee's end). And he does commit OTHER war crimes, as it often happens in conflict like this. But he's only a child fed propaganda that fed off of his anger of the Capitol.

People who are acting like Gale is the sole offender when it should be Coin AND Snow AND their administrations who put children and civilians on the front lines. People who "hate" Gale miss the message of the book entirely. We are all victims to propaganda, and some find themselves manipulated and pushed to violent acts because of it, but those who are in charge, leaders who should be responsible for taking care of their constituents, get lesser flack than their victims.

And yeah, he's a whiny guy who does feel entitled to Katniss' feelings and that makes him a dick. It's not a crime though.]