HARTFORD, Conn. - The families of nine people killed in the Newtown school massacre filed a lawsuit against the maker and sellers of the Bushmaster AR-15 rifle used in the shooting, saying the gun should not have been sold for civilian use because of its overwhelming firepower.

The lawsuit alleging wrongful death and negligence was filed in state court and announced Monday - the day after the second anniversary of the shooting, which left 20 children and six educators dead and became a rallying point for gun-control efforts.

In addition to Bushmaster, the defendants are Camfour, a firearms distributor, and Riverview Gun Sales, the now-closed East Windsor store where the gunman's mother purchased the Bushmaster rifle in 2010. Messages seeking comment from the defendants were not immediately returned.

The complaint says the gun allows shooters to inflict "unparalleled civilian carnage."

"In order to continue profiting from the sale of AR-15s, defendants chose to disregard the unreasonable risks the rifle posed outside of specialized, highly regulated institutions like the armed forces and law enforcement," the plaintiffs wrote in the complaint.

The so-called AR-15 rifle was first built by Armalite for military use, but the design was later acquired by Colt, which in the early 1960s began marketing the semiautomatic AR-15 rifle as the civilian version of its fully automatic M-16.

Many other companies have since begun manufacturing and selling AR-15-type rifles. The weapons are popular in shooting competitions due to the light weight of the gun and ammunition and the weapon's accuracy.

Bill Sherlach, whose wife, Mary, was killed in the shooting, said he believes in the Second Amendment but also believes that the gun industry needs to be held to "standard business practices" when it comes to assuming the risk for producing, making and selling a product.

"These companies assume no responsibility for marketing and selling a product to the general population who are not trained to use it nor even understand the power of it," he said.