The Jerilderie letter would be almost completely obsolete for an historian attempting to assess whether Ned Kelly was a hero or a villain. An historian should look at society's response to Ned Kelly when searching for such information as the belief that someone is a hero or a villain is completely subjective, and the closest anyone can come to an answer is to reach a consensus. The Jerilderie letter can at most, give us information about Ned Kelly's life, though whether that information is reliable or not is yet to be seen.
The Jerilderie letter was dictated by Ned Kelly and written down by one of his associates, Joe Byrne, sometime in 1879 CE. It was aimed it towards multiple audiences and this could have greatly affected Kelly's motives in writing the letter. Kelly wrote to the authorities of the time, trying to prove his claim of innocence. He also wrote to the people of Victoria, hoping that they also would view his actions as just.
...the public could not do any more than take firearms and assisting the police as they have done, but by the light that shines pegged on an ant-bed with their bellies opened their fat taken out rendered and poured down their throat boiling hot will be cool to what pleasure I will give some of them.
Kelly warned the people of assisting the police, denouncing them, threatening them and claiming that they should support him in his quest. He wanted to be seen as a "freedom fighter" in the eyes of the people, but also in the eyes of history. He attempted to show that he was not a villain, but a hero, fighting against the unjust, biased police et al.
Ned Kelly wrote the Jerilderie letter in the vain hope of justifying his...