In the 2007 movie There Will Be Blood, starring Daniel Day-Lewis, the main character -- Daniel Plainview -- puts a bullet into his "brother's" head when he discovers that the man isn't really his brother, but an impostor.
The killing was certainly unjustified. The man had stolen nothing and professed to be Plainview's friend. In fact, the man had saved Plainview's life when Plainview's kid set the house ablaze. Plainview should have just told him to get lost.
What was the point of killing the man?