The link you provided shows that no swab was taken from Trayvon's knuckles. They were left out in the rain (for 3 hours, I think though you can correct me if I'm wrong), giving plenty of opportunity for any VISIBLE blood there might have been on his knuckles and hands to wash off.
Bear in mind that Trayvon Martin's skin was fairly dark. Visually, blood would not show up on his darker skin nearly as easily as it would show up on the hands of a Caucasian person.
I suspect there were traces of blood there that might have been detected with a DNA swab. But since they weren't visible, and since whoever took the swabs wasn't totally on top of his game, those swabs were never taken.
As for Zimmerman's DNA on Martin's clothing, the only place it might show up would have been on Martin's sleeves. Even that seems unlikely, as Zimmerman, even with a broken nose, wasn't bleeding that much. Not from the face, anyway.
I don’t doubt Trayvon was beating Zimmerman. But what if Trayvon felt threatened by Zimmerman and was defending himself?
"What if" is the stuff that an acquittal is made of. It's reasonable doubt.
That said, there is no evidence for it.
As I've said before, if Trayvon felt threatened, all he had to do was continue home and go into the apartment. He had a full 4 minutes to cover a pretty short distance.
There is no evidence that Zimmerman pulled a gun on him. If he had, I seriously doubt that Martin would have struck him in the face. If he had attempted to do so, the instant result would have been a gunshot. Even if Martin had landed a punch, we would've had a gunshot early in the encounter. That's not what happened. We had 40 seconds of screaming (which is an eternity) followed by a bang.
Nor is there any evidence that Zimmerman ever struck Martin. No bruises recorded. No evidence of blows. Not to Martin.
Martin's only injuries were a scraped knuckle and a fatal gunshot wound, compared to MANY lacerations on Zimmerman.
All the physical evidence is consistent with Zimmerman's account.
ABSOLUTELY!
I wonder if that genius witness Rachel ("no, sirrrr/yes,sirrrrrr) was egging TM to take down the "creepy ass cracker". I think she even said GZ might be a homosexual wanting to rape TM, IIRC.
Maybe that is why TM circled back. There are so many scenarios in this travesty against justice and truth. Again, IMHO. I think her name was something like Rachel Jeantel. If you saw her, you'd know immediately who I'm talking about! Not forgettable for all the wrong reasons.