The author is a father of a gun-related murder victim, which makes the letter even more appealing and persuasive.
The author used Ethos by complimenting the reader and being polite in the introduction. He also made the reader feel sorry for all the victims of gun-related murders. Furthermore, the author made the reader think carefully about the decision whether to support the gun control legislation, by "saying" that he would be responsible.
There is a lot of Logos used in this letter. The author gave a lot of logical facts about how many people were victims of gun-related murders, that 60% of murder victims in the U.S. in 1994 were killed with firearms, etc.