Alex Kraile is the director of the student film, Marble Hornets. As the shooting progressed, Alex eventually got paranoid and even violent.
Entry #37 indicates that Alex may have been stalked by the Operator long before production of Marble Hornets began, at age four or five, making that possibly the first recorded appearance of the Operator in Alex's life. It is only when he began shooting for the film was when fate had caught up to him. Alex's birthday is April 4, which is a huge date in the Marble Hornets series.
Shooting Marble Hornets
Alex was the director of Marble Hornets, while Jay supervised the scene. As Alex shot the scenes for Marble Hornets, he started becoming paranoid, distraught, and even exhibiting signs of Slender Sickness. Alex began to film himself exclusively as he starts to notice the Operator's presence. The Operator almost exclusively stalks Alex in Marble Hornets and is almost always where Alex is. It appears that at first, Alex may have been attempting to find the Operator to understand it, but currently seems to be under it's influence and working for it.
In Entry #49, we see Alex delve deeper in the woods for something and mistakes a man for Jay. He kills the man with a rock similar on how he nearly killed Tim with a rock as well. Strangely, Alex doesn't even try to kill Jay the next time he sees him, but his intentions are apparently revealed in Entry #52 where he has Jay and Jessica at his mercy only to be stopped by Masky.
Its unclear whether this is Alex's free will at work here, but it does seem as if he is being influenced by the Operator as seen in later entries. (Entry #56, Alex acts calm and rational, later attacks Tim, Operator present) Alex used to be a humorous and kind person, but it appears as though the Operator has changed that.
According to Jay, Alex probably intended to 'tie up loose ends', suggesting that this is Alex's free will at work here and the Operator is merely helping him tie up said loose ends. By tying up loose ends, Jay refers to Alex's strange choices like killing the man in Entry #49, dragging Brian's limp body off in Entry #51 instead of getting help, breaking Tim's leg, attempting to kill the Masked Man from Entry #45, and finally holding Jay and Jessica (Who arguably were both innocent) at gunpoint in Entry #52.
Alex, however, does claim that he was looking for his girlfriend, Amy, who appears to be missing. However, it is unclear if Alex is continuing the search or tying up more loose ends.
Being Alex's friend at the time, Jay got the tapes but eventually forgot about them, only to remember them years later. However, he began to review the tapes on YouTube and even plan his moves on there as well. Also Jay later was confirmed to be Skully on the to-the-ark youtube channel. Maybe a reason Alex had shot and killed him.