This is all still quite recent. Do we know they were hers? Could they have belonged to one of the sons, or the father?
No, the guns were "registered" to the mother.
Of course, Connecticut (like Pennsylvania) technically does not have firearms "registration." But Connecticut does require that ALL sales of firearms through FFLs, and all sales of handguns between private parties, must be called into the State Police Firearms unit for a transaction approval before the deal can be (legally) completed. The state has a 4-part form that asks pretty much the same exact questions that are on the Federal 4473, with the names and addresses of both the buyer and the seller. One copy of this state form goes to the buyer, one copy goes to the seller, one goes to the state police, and the fourth copy goes to the local police in the municipality of the buyer.
So, except for the "loophole" that long guns may be sold privately without state blessing, there is an official record of pretty much all gun sales in CT. So it's not hard to see how they tied the guns to the mother. Did she buy them for herself? Unlikely. The 20-year old shooter was known to have enjoyed violent video games. At 20, he was not old enough to buy handguns himself. So it's probably a safe guess that Mommy indulged her autistic son's fantasies by buying the guns he wanted for him. If she then gave him the handguns rather than keep them under her own control ... she broke the law, and ultimately paid for it with her life.
The professional psychologists refuse to admit it, but IMHO these violent, shoot-em-up video games are responsible in large measure for the huge increase in violence (and "gun violence") this country has experienced in recent years.