After searching around, my source for this information is MacRanger:
According to a source with knowledge of the investigation in to the Trayvor Martin shooting, three witnesses have now been identified that all confirm that Martin was on top on Zimmerman before he was shot. Details are sketchy, but some of the witnesses confirm hearing Zimmerman yelling for help and one witness states that Martin could be heard yelling at Zimmerman, calling him a “honkey” and saying “You’re going to die” or some words to that effect.
The problem is that MacRanger has proven to be an unreliable source of inside information. He said that he had information that Zimmerman wasn’t going to be charged, but he was completely wrong about that. (But if you want to give MacRanger the benefit of the doubt, perhaps someone at Angela Corey’s office saw all of the evidence, including the exculpatory evidence, and couldn’t possibly believe that Zimmerman could be charged based on that, and relayed that impression to MacRanger.)
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“Turambar” pointed out in a comment that MacRanger also gave us false information about Trayvon Martin not have ice tea and Skittles on him. In fact, he did.
I have to conclude there’s a good chance that MacRanger is just making stuff up.