After going through a dozen more memory cards, it has become clear to me that the vast majority of the footage is completely unrelated to Alpha Decay.
At some point, it seems as though Alexa began to film herself exclusively.
The following clips are taken from the cards I've reviewed most recently.
Cut from black. The first clip: a camera is focused on Alexa's knee as sounds of paper being shuffled and torn are recorded out of viewing range. As the shuffling continues, a strange blue line tears through the image at the bottom of the clip. She gets up for a moment, shuffling continuing further in the background, then sits back down on the couch.
The second clip: Alexa is outside again, perhaps in the same place she visited during Entry 2. This time, it is twilight. Trees are just barely visible in the dim light as the camera moves from side to side, as though she is looking for something.
The third clip: Alexa confers with an off-screen companion in the background as the floor of a store comes into focus. She approaches a shelf with new memory cards on it, and picks out an entire pack before walking away.
The fourth clip: We finally see Alexa herself in front of the camera. Perhaps someone knows this girl. The camera is propped up on the desk at an angle while she contemplates a large screen projected by her iHolo. She reaches forward intermittently to tap on her projection keyboard, but jumps up with a start -- Alexa realizes that the amount of space on her camera memory card is about to be filled up. She scoots her chair further from the camera and reaches for a new pack of cards, unwraps one, then pulls her chair back towards the camera to replace it at the very moment the old card runs out.
The fifth clip: Alexa is outside in a park again, but now it is daytime. The clip begins with a pan back and forth between the trees, but the camera tilts back down to ground level.
The sixth clip: It is night again. Alexa's camera is propped up on the dashboard of her car, recording her as she drives. The shot is dark, and the angle of the camera is such that it only captures the bottom half of her face.
The seventh clip: Alexa is in the same desk area that appeared in the fourth clip, but now she is faced away from the camera, looking intently out her window. Her iHolo chimes, bringing her closer to the lens, but she only attends to it in order to dismiss the call. She takes the camera off the desk and is in the process of relocating it for a new angle as the picture cuts back to black. Narration appears again.
From what I've seen so far, many of these tapes could contain nothing of value.
For some reason, Alexa wanted to have a camera on herself at all times.
The clip from Entry 1 is still the best lead that I have.
Cut to black. End of entry.
OOC NOTE. Plot, dialogue, and video sourced and adapted from Entry 3 of Marble Hornets on YouTube. Watch at your own risk.