How's this? To frame Alex, they had to be on the property. This goes to motive. They want to watch Alex suffer through all this. They had opportunity, dark, rainy night, open gate, plenty of pines to hide behind. Means? That's trickier. They had to count on Paul setting his gun down at some point. It is possible the other gun they knew was in the white pickup. This could explain how the truck got off the property--they could have stolen it and abandoned it to get themselves farther away from the crime scene quickly. I know that's a stretch. They had plenty of time to get rid of the guns, whereas Alex did not have much time at all because he had to establish his alibi at his mom's house and keep making calls to his wife, change clothes, wash himself, etc.