I believe it will come out that the two of them knew each other. It’s pretty hard to imagine running down, backing over, stabbing multiple times and then kissing some random unknown person.
I’m thinking it’s possible that “Karon” had propositioned Steve Anderson (as in — “hey sweetie, wanna “date””?) and was turned down (perhaps harshly) — then “she” took this as a “diss” and acted accordingly (in his delusional world)