Some facts I gleemed from this.
1. He sold how to make silencer/full auto books at gunshows.
2. There were several 80% receivers in the proccess of being made into guns in his home.
3. He had worked on this gun extensively.
4. The selector switch freely rotated past the semi position, and into the 3rd/auto position. And fired full auto.
Now, any of those is legal, save 4, but when you add them all up, it really looks suspicious......
"If there must be trouble, let it be in my day, that my children may have peace"