This article shows excerpts from some of the letters I was wondering about: http://www.huffingtonpost.com/2013/10/18/jordan-davis-shooter-michael-dunn_n_4123805.html
I'll quote one below:
There are others of a similar theme, sent to various people.
The mere fact that he did not call the police screams guilt to me. If he was sooo afraid that these thugs were coming after him he should have called 911.
:gavel: