You are misinterpreting the “reasonable doubt” instruction given to juries. It is not an invitation to construct as many imaginary scenarios as you can where the defendant might be innocent. It is to take the scenario being given to you be the prosecution and determing whether the scenario is plausible and sufficiently backed by evidence to where you have no doubts in its veracity. If you do have any “reasonable” doubts, then you are required to vote not guilty. It is one of the few worthwhile ideas in our injustice system.
Sean, although you feel there is reasonable doubt that Zimmerman shot Martin to death based on a threat to his life, do you also feel that there is reasonable doubt that Zimmerman stopped his car, which had working headlights, and got out of the car to check a street sign:
(1) In his own neighborhood;
(2) Where he had been living for years;
(3) Where he had been working on the neighborhood watch for those years, and called in dozens of reports about the locations of people in the streets of that neighborhood;
(4) When the person he was supposedly concerned about the police catching was, at the same time, "on the move" away from that very street.
Also, after he stopped the car, Martin kept walking, and Zimmerman went over to check the street sign, did Zimmerman then "walk" up to Martin? With Martin walking in the other direction?
Zimmerman reported, at one point, that he walked up--that he didn't have to jog or run to catch up, even though he'd first stopped his car, put it in park, taken off his seatbelt, gotten out, shut the door, gone to the street sign, squinted at the sign, then turned around to continue pursuit. However, he later changed it to walking innocently down the street when Martin "jumped out of the bushes" and said something about "homie," at which point this fight started.
Your version of "reasonable doubt"--a version that depends on plausible human memory and behavior, as well as the 60-second minute--does not comport with Zimmerman's story. The only way he could have overtaken Martin in the rain, with a lead, after he'd been denied permission to pursue (especially after stopping his car to "check a street sign") would violate his story, because it would require, at the last, a brisk jog.
What his story spells out is that he stopped his car near Martin, asked the 911 operator if he could confront the suspect, and was then denied permission. When he was denied, he got upset, and got out of his car to go after Martin anyway. Martin saw a guy watching him in the car, plotting on the phone, and then the guy stopped the car, got out, and rushed at him with a gun. That is plausible "standing your ground," and a justified first punch in the nose. Zimmerman's actions, and the little mistakes he made in his story later (about why he got out of his car, how he caught up to Martin, and whether or not he was ambushed or just "walked up to" the kid), are the only portions of the story that are not plausible.
Oh, and have you ever had your head slammed into the concrete? Zimmerman got a bloody nose from getting punched, and some scuffles from when he tried to take the kid down afterward and got, as only a crude and sexist person might put it, "bitched." He did not get his head "slammed into the concrete"--his mild lacerations (widdle scwatches) came from a brief tussle--say, trying to keep a 140 lbs. dripping-wet 17-year-old from taking his gun away.
His injuries, and their quite-rapid healing, go along, reasonably, with what you'd expect from a fat coward playing rent-a-cop by stalking and attacking a black kid. This is why Zimmerman did not get an X-ray, or more importantly, a CT scan, for having his head violently and repeatedly slammed into the concrete. (From a medical perspective, there is no way he wouldn't have gotten told to have a CT scan if he'd actually gone in for such an experience). If Zimmerman had just gotten whacked like that, and had bleeding in the brain or an aneurysm, he should've had some after-effects, not the least of which would've been a legitimate concern about going to the doctor. Instead, he was able to calmly report things to the cops, go home, come back the next day, tell a slightly different version of the story with more violence, and not worry about his health at all. He reasonably did not go to the doctor because anyone examining him would've been able to tell it was just a few scratches, and that he didn't even have any bruising, or anything else that would've saved him from getting second-degree for attacking and shooting some kid.
That's why "reasonable doubt" does not actually mean "plausible"--it means luck, money, and popularity.