Thank you for the opportunity to assist you. I'm sorry about what's happened with your son.
I'd recommend contacting two organizations. First, the Florida Innocence Project. They help folks like your son with post conviction relief. The second organization is the Florida ACLU. They do similar work to the Innocence Project.
Gather all the materials you can related to your son's trial. A copy of the court's file, transcripts, witness interviews, depositions, etc. Have it all ready for the Innocence Project or the ACLU to review. They'll hopefully look over it and give you a straight up assessment of whether anything can be done to help your son.
Keep in mind that these organizations are in great demand. There are a LOT of people who need their help. So, they have to prioritize. It may be that one or the other will be unable to assist you due to funding or time constraints.
I hope my response has been helpful. If you have follow-up questions or concerns on this topic, please ask. I'll get back to you as quickly as I can, although I may not be online at the moment you respond. Otherwise, I hope you will rate my answer positively as that is the ONLY way I receive credit for my work, and doing so will NOT cost you an additional fee.
Best wishes to you,