Thursday's mass shooting on a college campus in Oregon came just weeks after the state recently tightened restrictions on gun purchases.
A law that went into effect on Aug. 9 requires background checks for transactions made between individuals and online. Previously, checks were mandatory only for people seeking to buy a gun from a federally licensed dealer — at a gun store or gun show.
It is not clear where or when the shooter in Thursday's attack obtained his weapon nor whether the new law would have had any impact.
Gun-control advocates said the new measure would prevent criminals and the mentally ill from buying guns.
Left unclear, however, was how the expanded checks would be enforced.
The law requires a private seller and buyer — unless they are related — to go together to a licensed dealer who would conduct the check, for a fee. But critics of the legislation pointed out that someone accused of skirting the law could easily claim the sale was conducted before the new requirements became law.
Sheriffs in some rural counties said they wouldn't enforce it at all, saying it would require too much work.
This article first appeared on NBCNews.com.