Interesting theory. If his role was 'cleanup' that might explain the porch perp's lackadaisical style, his extreme layering to avoid DNA transfer, and a stuffed backpack, which could contain tools of his trade such as a sack or tarp.
If this theory has any legs, it could imply an accomplice inside already, having entered another way. And as an OP opined re: odd sized tire tracks on the driveway, perhaps NG was taken out in a trash can that the 'cleanup' guy brought.
It would also imply, if at all close to the truth, that NG's disappearance and the ransom circus may be separate crimes.
I just have to wonder if NG walked into a home invasion when she returned from dinner on 1/31. Either the perps were already inside or they were waiting for her to return. And sadly, perhaps she was murdered to eliminate a witness. Unless the perp(s)'s intent was to kill her.
Total speculation and my own opinion. Since we're on Day 12, it just makes me wonder if this was not an abduction.