1997 special editions aside, Star Wars fans know that Han Solo shot Greedo first. However, when George Lucas revisited the original trilogy, he made it so Greedo shoots Han Solo in the booth at the Mos Eisley cantina a fraction of a second before Han Solo blows the blue bounty hunter away. Somehow, he misses at point blank range. Putting that aside, the generally accepted truth from fans of the franchise is that Han Solo kills Greedo in a bit of preemptive, badass self-defense. But is that legal?
To answer that question, we need look no further than the laws we accept in society for self-defense, which rest somewhere outside of Jabba's Palace. The answer lies within the Model Penal Code. While reading all of the legal jargon may be a bit exhausting, it's actually not terribly difficult to sort out. Here's what the Model Penal Code has to say about the use of deadly force in self-defense.
"The Code specifically sets forth the situations in which deadly force is justifiable: when the defendant believes that such force is immediately necessary to protect himself on the present occasion against: 1. Death; 2. Serious bodily injury; 3. Forcible rape; or 4. Kidnapping. The Code prohibits the use of deadly force by a deadly aggressor, i.e., one who, 'with the purpose of causing death or serious bodily injury, provoked the use of force against himself in the same encounter.'"
It's important to note that there's a "retreat rule." While the actual legal explanation for this rule is lengthy, the important bit is that if you can get away without killing someone to defend yourself, you need to exercise that option before you just blow them away. In Han Solo's case, he was pretty much trapped in the booth with Greedo, who had his gun pointed at him from the start. So retreating wasn't a real option.
Now, the other important bit to take into account has to do with what is known as "reasonable belief." This legal clause states that a person is justified in using deadly force to protect oneself if they believe that force is needed to "repel an imminent unlawful attack." Here's the full section of the Model Penal Code.
"The privilege of self-defense is based on reasonable appearances, rather than on objective reality. Thus, a person is justified in using force to protect himself if he subjectively believes that such force is necessary to repel an imminent unlawful attack, even if appearances prove to be false. Courts are increasingly applying a standard of the "reasonable person in the defendant's situation" in lieu of the "reasonable person" standard. Factors that may be relevant to the defendant's situation or circumstances include: 1. The physical movements of the potential assailant; 2. Any relevant knowledge the defendant has about that person; 3. The physical attributes of all persons involved, including the defendant; 4. Any prior experiences which could provide a reasonable basis for the belief that the use of deadly force was necessary under the circumstances."
With all of that taken into account, it looks like Han Solo was perfectly justified in frying Greedo in Star Wars: A New Hope. Yes, Han shot first and, according to the fine folks at The Legal Geeks, we now know that he was perfectly justified in doing so, from a legal standpoint. At least when it comes to applying our Earth laws to Tatooine. Their legal system may differ quite a bit.