US shooter armed with extensive weapons

This 2005 photo provided by neighbor Barbara Frey and verified by Richard Novia, shows Adam Lanza. Authorities have identified Lanza as the gunman who killed his mother at their home and then opened fire Friday, Dec. 14, 2012, inside an elementary school in Newtown, Conn., killing 26 people, including 20 children, before killing himself. Novia was the school district’s former head of security and he advised the school technology club that Adam and his older brother belonged to. (AP Photo/Barbara Frey)

NEWTOWN, Connecticut – The gunman in the Newton, Connecticut, school shooting was prepared for a massacre.

An official with knowledge of the investigation told The Associated Press three weapons were found inside Sandy Hook Elementary School and a fourth weapon was found outside.

These weapons are critical evidence as investigators try to unravel why Adam Lanza killed 20 children and six school workers Friday after killing his mother at their home. The official was not authorized to speak on the ongoing investigation and spoke only on condition of anonymity.

The murder weapon:

— Bushmaster .223-caliber: lightweight with a high capacity, it also is popular with law enforcement and the military, and is commonly seen at shooting competitions. Two men convicted in a series of sniper killings in the Washington, D.C.-area in 2002 used a Bushmaster

.223-caliber rifle that they fired from the trunk of a car at randomly picked victims. Some models have a detachable magazine that can hold up to 30 rounds. The medical examiner in Connecticut said it appeared all the children and school staff were shot with the same high-powered rifle, some repeatedly, some at close range.

Also found in the school:

— Glock 10 mm: a larger and more powerful weapon than the widely popular 9 mm, it is in many respects similar to the 9 mm. It is a lightweight and comparatively affordable weapon that is often used for target shooting and for personal protection.

— Sig Sauer 9 mm: considered an upper-tier, quality product, it’s comparatively expensive, and its range of uses include elite military and police units.

The Bushmaster and two other weapons were found near the body of Lanza, who killed himself at the school.

It was not clear the make of the weapon found outside the school.

Investigators are combing gun shops and ranges in the area, and looking into the ownership of the weapons involved. Lanza’s mother had legally registered four weapons, and his father had two.

Three other guns have also been recovered, but it was not clear where they were found, the official told AP. They were a Henry repeating rifle, an Enfield rifle and a shotgun.

Also unclear is which gun the 20-year-old Lanza used to take his own life or his mother’s. The Lanzas autopsies are scheduled for Sunday.