WASHINGTON — In the days since the massacre at Sandy Hook Elementary School in Newtown, Conn., a shell-shocked nation has looked for reasons. The list of culprits cited include easy access to guns, a strained mental-health system, and the ‘‘culture of violence’’ — the entertainment industry’s embrace of violence in movies, television shows, and, especially, video games.

‘‘The violence in the entertainment culture — particularly with the extraordinary realism to video games, movies now, et cetera — does cause vulnerable young men to be more violent,’’ Senator Joe Lieberman, Independent of Connecticut, said.