"At no time did George follow or confront Mr. Martin. When the true details of the event became public, and I hope that will be soon," the letter said, "everyone should be outraged by the treatment of George Zimmerman in the media."
"I asked [the police], 'Well, did you check out my son's record?'" Tracy Martin told ABC News in an interview Sunday. "What about his? ... Trayvon was innocent."
Trayvon Martin's Family Seeks Justice
Trayvon Martin had no arrest record or disciplinary action for violence as a student in North Miami's Krop High School.
On Monday, Lee, seeking to head off racial unrest, tried to reassure the public that his department was doing all it could to reach a fair conclusion, as some in the crowd heckled him by saying, "a little black boy is dead."
Lee's department said it plans on passing its investigation over to the state's attorney office to determine whether to press charges against Zimmerman.
Trayvon Martin's parents described him as the kind of son who, even at 17, allowed his parents to kiss him publicly.
"That was my baby, my youngest son," his mother, Sybrina Fulton, told ABC News in an interview in Miami. "He meant a lot to me, I don't think the police department really understands that. ... I need justice for my family, I just want justice for my son."
Fulton is incensed that Zimmerman left his car despite being urged by dispatchers to stay put.
"My son didn't do anything," she said. "He was walking home from the store. Why would the neighborhood watch guy would have a weapon? ... It's just crazy. You are supposed to watch the neighborhood, not take the law into your own hands."
ABC News' Matthew Rosenbaum contributed to this report.