It looks like he has a gun or something down the back of his pants. As soon as he sees the doorbell cam he bolts. This is local to me. My son lives a couple blocks away from where this happened. He goes to Cal Poly University and it's only a half mile away. He's wearing gloves and has what some believe may be a syringe in his mouth. He rang the bell and then hung on to the door knob.
https://www.facebook.com/SLOStringer/videos/1007067969405640/
https://www.facebook.com/SLOStringer/videos/1007067969405640/