HARTFORD, Conn. — The families of nine of the 26 people killed and a teacher wounded two years ago at the Sandy Hook Elementary School filed a lawsuit Monday against the manufacturer, distributor and seller of the rifle used in the shooting.

The negligence and wrongful death lawsuit, filed in Bridgeport Superior Court, asserts that the Bushmaster AR-15 rifle should not have been made publicly available because it was designed for military use and is unsuited for hunting or home defense.

“The AR-15 was specifically engineered for the United States military to meet the needs of changing warfare,” attorney Josh Koskoff said in a release. “In fact, one of the Army’s specifications for the AR-15 was that it has the capability to penetrate a steel helmet.”

In addition to Bushmaster, the defendants are Camfour, a firearm distributor, and Riverview Gun Sales, the East Windsor store where the gunman’s mother purchased the Bushmaster rifle in 2010.