Terrible story. I agree, I think taking the knife suggests some premeditation rather than an act of spontaneous rage. I don't think it necessarily excludes regret, for what ever reason we all regret doing stupid things. I do worry that folks don't have a good understanding of the consequences of their actions nowadays, especially when they grow up in our virtual digital culture where you respawn after dying as much as you like in games or push the undo button to correct mistakes you make on the computer. There is no undo button in life - my rule #7 for a happy life.
I wonder how many people take a knife or a gun, and start heading somewhere , with intent to kill, and then somewhere along the way think better of it and turn around.