An innocent person will say that he did not do it, early on.
What to look for: "I did not kill..." or "I did not shoot", or "I did not..." with the specific allegation.
The letter is here:
Remember, one can truthfully say:
"I am innocent" because he has not been proven guilty.
"I am not guilty" because he has not been proven guilty in a court of law.
"I am a good person" because he may believe it so...
but does he plainly tell us, early and perhaps often, that he did not do it?