Though I have just heard this in passing conversation and have not confirmed it - I was told that there are ~20 reported incidents of Zimmerman tailing black 'suspects'. Supposedly, the Defense tried to prevent the Prosecution from allowing them to testify, but I believe 5 of them are allowed to for whatever reason.
Personally, if I was the Defense, I would allow every single one of them to testify and then point out the fact that, of the 21 people he's tailed, only one of them got shot. Why do you supposed that is?