Examining the Evidence
The enigmatic verse of Bereshit 4:8 reports on the first killing and death in history:
וַיֹּאמֶר קַיִן אֶל הֶבֶל אָחִיו וַיְהִי בִּהְיוֹתָם בַּשָּׂדֶה וַיָּקָם קַיִן אֶל הֶבֶל אָחִיו וַיַּהַרְגֵהוּ.
Coming in the wake of a bitter dispute between Kayin and Hevel, it is natural to assume that this was a case of intentional and, perhaps, premeditated fratricide. But before we jump to this conclusion, let us first consider the textual evidence we possess regarding the punishment meted out by Hashem, Kayin's appeal of his sentencing, and his motivation for and possible premeditation of the act itself.
Does the Punishment Fit the Crime?
Intentional murder is a capital crime, and thus, if Kayin deliberately killed Hevel, one might have expected Hashem to administer the death penalty. Yet, Kayin is spared such a sentence, and is instead informed that he will be cursed from the land and forced to live the life of a wanderer. This punishment is very reminiscent of that given to the inadvertent killer who is exiled from his home. Did Kayin receive this less severe penalty because of technical reasons, or were there fundamental mitigating circumstances which made his act more similar to that of an unintentional murderer?
Reaction to Sentencing
After receiving his sentence, Kayin responds to Hashem:
(יג) וַיֹּאמֶר קַיִן אֶל ה' גָּדוֹל עֲוֹנִי מִנְּשֹׂא. (יד) הֵן גֵּרַשְׁתָּ אֹתִי הַיּוֹם מֵעַל פְּנֵי הָאֲדָמָה וּמִפָּנֶיךָ אֶסָּתֵר וְהָיִיתִי נָע וָנָד בָּאָרֶץ וְהָיָה כָל מֹצְאִי יַהַרְגֵנִי. (טו) וַיֹּאמֶר לוֹ ה' לָכֵן כָּל הֹרֵג קַיִן שִׁבְעָתַיִם יֻקָּם וַיָּשֶׂם ה' לְקַיִן אוֹת לְבִלְתִּי הַכּוֹת אֹתוֹ כָּל מֹצְאוֹ.
Though Kayin's words are open to interpretation, his reaction seems somewhat surprising. If Kayin was an intentional murderer deserving of death, how does he have the temerity to protest that his punishment was overly severe and might bring about his death? And if Kayin's complaint had no merit, why does Hashem feel compelled to address his grievance by providing Kayin with a special protective sign?
Context and Motivation
Finally, the Torah gives no indication that Kayin killed Hevel in the heat of the moment, as an immediate response to Hashem's rejection of his sacrifice. To the contrary, in the interim Hashem first speaks to Kayin, Kayin speaks to Hevel, and they go out to the field together. Did their discussion in the field begin innocently, but somehow escalate into a murderous brawl or, alternatively, was the conversation part of Kayin's premeditated plot to catch his brother by surprise? After just being chastised by Hashem, though, it seems odd that Kayin's first action would be to orchestrate the murder of his brother. Did he really think that doing so would achieve his goal of ingratiating himself with Hashem?