There's no record of the weapon used or of any interest in what it might have been. At issue is not the weapon but the killing. It was perhaps because of jealousy, but we don't really know. After Qayin (Cain) killed his brother Havel (Abel), no one lamented over the weapon.
Our deeper question, why might he have done it? What was the real reason?
Heart issues remain the more important ones, but they're hard to face and even harder to address effectively. It's perhaps understandable that we might move on to less relevant targets and focus our efforts there.
The Arab Spring, Tahrir Square, Egypt - Christians
guarded Muslims, and Muslims guarded Christians
during the violent times.
In any endeavor, the hard questions are often the more important.
Falling back on gun control as an easier solution ignores the obvious, that murderous behavior is not brought about by the available weapon.