Can you show me where in MA law it states that?
It doesn't say that in the law, but he's working off the doctrine of "constructive possession". The thing is, I know of no case law in MA to back up that assertion.
For example, in fed/BATFE realm if someone has a short barreled AR upper and no registered SBR lower to mate it to, but one or more non-registered, non-NFA lowers
around, the assumption is that BATFE would consider someone owning an SBR in that circumstance via constructive possession.
Constructive possession rarely appears directly in a law, but is often used by a prosecution to make it look as though the person charged, while not having said "prohibited device" etc, was not more than a few simple steps away from having it. The feds use it a lot. Problem is that it's a generic concept- eg, obviously the authorities can't say that everyone with a gasoline can is an arsonist, on the other side of the coin, either.
I think whether someone could actually get charged for constructive possession or not under MA law is a matter of to what degree some jackoff prosecutor would
go to persue the issue; and chances are if it became an issue the person defending the charges likely has bigger issues to deal with anyways.
One interesting thing that could make constructive possession fail in MA is how a "firearm" is defined. There's that whole "readily capable of discharging a shot"
thing, whereas on the other hand in fed realm a firearm can be a piece of metal.
-Mike