Witnesses that change their story, just neutralize themselves. Possible that the eyewitnesses end up being zero sum, and all that’s left is physical evidence. Still a win for George.
I think it's better than that.
Witness 12 already said she was influenced by the media. Any negative information that came out after the media blitz could be attributed to that. That would also bolster Zimmerman's case that the case has been irrevocably tainted.
Even better - HOW did these witnesses become tainted? Think like a lawyer - they saw the news stories, which came from Sharpton and Jackson, which, in turn, came from Crump and Company. So, how would you show HOW the witnesses were tainted? You'd introduce the stories, and get source of the stories to testify. You could then point out all the lies they told in the press - Crump's ever-changing narrative. You could get the media editors on the stand and ask them why they gave creedence to Jackson and Sharpton, whether they knew about Brawley, Duke, etc. You could ask them whether, based on their years of experience in the news industry, if they would expect these stories would influence public opinion. All your doing is establishing how the witnesses were exposed to misleading information. You also get the race-baiters on the stand, under oath, to admit that the original narrative was wrong.