Warning: wall of text incoming
Lets review this case methodically and look at the decision that the judge has made. Under the 1998 Florida statutes "A person is justified in the use of force, except deadly force, against another when and to the extent that the person reasonably believes that such conduct is necessary to defend himself or herself or another against such other's imminent use of unlawful force. However, the person is justified in the use of deadly force only if he or she reasonably believes that such force is necessary to prevent imminent death or great bodily harm to himself or herself or another or to prevent the imminent commission of a forcible felony." (source: http://www.self-defender.net).
So the question of whether the judge made the right decision as to whether Jorge Saavedra killed Dylan Nuno in an act of self defence motivated by fear of imminent death or great bodily harm.
Lets examine the implication of the knife itself, as many people have already commented that this means that the attack was premeditated thus murder.
Jorge Saavedra brought the knife onto the bus, which suggests premeditation. However, the fact that Saavedra repeatedly attempted to disengage and de-escalate from the confrontation which was to occur at the final bus stop suggests that it was not his intention to aggressively utilise the knife (as in use it as an advantage in the upcoming altercation), but instead was carrying the knife defensively (to use as an escape option or as a bargaining chip when trying to prevent being beaten). Remember here that I am not debating whether it was legal or right of Saavedra to be carrying a weapon, I am trying to discern whether he believed he was in danger of imminent death or great bodily harm.
Now lets move on to the actual chronology of the incident.
Nuno had been involved in both altercations and verbal abusive with Saavedra multiple occasions prior to the final conflict. These incidents were frequent and severe enought to make Saavedra continually avoid contact with Nuno by skipping school and/or avoiding the bus. Thus merely being on the bus, let alone near Nuno would be enough to heighten stress levels in Saavedra. As the bus trip wore on Saavedra was repeatedly prevented from disengaging from the future conflict scenario, each time increasing the stress that he was under. The body's natural reaction to stress is provided by the sympathetic nervous system in the form of adrenalin, causing numerous physiological changes such as auditory exclusion and tunnel vision. However, the most prominent aspect of the sympathetic nervous systems responses is so called 'flight-or-fight' (source: On Killing, Lt.Col. Dave Grossman). This means as Saavedra steps of this bus he is already amped and ready to go.
Now this brings us to the physical altercation itself and the mindset which Saavedra found himself in as the conflict progressed.
Firstly, Saavedra is followed off the bus by Nuno and several friends. Saavedra is now outnumbered by larger and older boys. Even if the others were not going to partake in the violence their mere presence lends itself to Nuno's power in the situation and increases the stress which Saavedra is undergoing. Nuno then proceeds to strike Saavedra in the back of the head. Now a headshot, particularly one which you don't see coming, is going to rock you (source: personal experience), but more importantly it is now the breaking point in a psychological build up which began way before the first punch was thrown. All that stress he had been under up to this point is now unleashed as his body goes into emergency mode.
Now according to the judge Saavedra was under attack from the moment he was hit in the back of the head until he began to stab Nuno. Unfortunately we do not have any video footage of the fight itself so we cannot be sure of the severity of the attack Saavedra was subjected to before he began to stab Nuno so here we must depart fact and begin speculation (though to be fair my dramatic interpretation of Saavedra's mental state was also speculation, however much more well informed than the following.
Nuno used an ambush attack to catch Saavedra off guard, he was not interested in a 'fair' fight (a contest if you will). Rather, he was attempting to showcase his dominance over Saavedra by humiliating him with a beating. It is impossible to discern whether Nuno was going to kill Saavedra or just going to 'smack him round a little' but at this moment Saavedra is under attack, his mind in code black, and he sees no possible 'flight solution' to save himself from attack. The fact that Saavedra was carrying a knife to begin with suggests that he feared that the altercation would be severe enough to warrant the carriage of a lethal weapon (in his own mind not legally). Thus Saavedra is now in a state of fight-or-flight his escape routes denied to him and reeling from an ambush style attack which he suspects may result in at least major bodily damage to his own person. In this situation Saavedra now draws his knife and attacks Nuno stabbing him 12 times and dealing two fatal blows.
Now allot of people have been arguing that 12 stabs seems excessive. In most stabbing situations you need to realise how quickly a knife strike can occur. (source: [WARNING: BLOOD AND DEATH] http://www.youtube.com/watch?v=J6gcFPjdwiI, ignore the stupid commentary ) watch many strikes the attacker gets in before being shot (and that includes the time it took to navigate obstacles and change targets). Now admittedly we don't know whether Saavedra used the wild slashes of an amature or the trained and controlled stabs of the knife fighting pro (I'll go with the former) however, I believe the section right before the attacker is shot at the end of the clip best represents what the knifing of Nuno would have looked like, a wild and rapid attack in which 12 strikes would have literally been a matter of seconds. During the attack itself Saavedra probably didn't even make the concious decision to continue stabbing Nuno, he merely continued to strike until the threat to his life was stopped, resulting in the death of Dylan Nuno.
Looking at the facts from this angle it is possible to see why it would be completely justified for the judge to clear Saavedra of his charges. I will admit I have made some assumptions: Saavedra's mental state, the nature of Nuno's attack and the nature of Saavedra's knife attack. However, I believe that these are not flying leaps to conclusions, but fairly balanced extrapolations of the facts present. As to the morality of the issue that is entirely up to the individual.
Do I think Saavedra should have been carrying a knife? No.
Do I think that Saavedra's actions were justified? Yes.
Do I think that the end result was a tragedy which left a young man, regardless of his character and nature, dead? Yes.