The act of stamping the numbers into metal changes the metal structure underneath stampings.
The serial numbers will be chemically recovered to find the origin and transferre to dealer and any buyer.
I know...
However, these two are idiots for opening their mouths to begin with. The way prosecutors are these days, they be lucky if some democrat appointee doesn’t charge them with “constructive intent” or some other bs...
I would have separated the lower receivers, for the ATF to take, and kept everything else to sell.