SANTA CLARITA (CBSLA) – A 16-year-old student who opened fire on his classmates last week at Saugus High School in Santa Clarita – killing two of them before turning the gun on himself — used an unregistered “kit gun,” authorities disclosed Thursday.

The Los Angeles County Sheriff’s Department reports that investigators determined that the .45-caliber semi-automatic pistol which Nathaniel Berhow used in the Nov. 14 killings was assembled from separate pieces, as opposed to being purchased as a whole gun from a manufacturer. A kit gun also goes by the term “ghost gun.”

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“The report on the firearm indicates that the handgun used in the assault was not manufactured conventionally and may be some form of a ‘kit gun’ ie. assembled by a consumer rather than a manufacturer, from pieces bought separately,” the sheriff’s department wrote in a statement.

Members of law enforcement walk at Saugus High School after a shooting at the school left two students dead and three wounded on Nov. 14, 2019. (Getty Images)

Furthermore, investigators are unsure who purchased the parts or who assembled the gun.

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Fifteen-year-old Gracie Anne Muehlberger and 14-year-old Dominic Michael Blackwell were killed and three of their classmates wounded when Berhow opened fire on his 16th birthday in the quad of Saugus High. Berhow passed away the following day from a self-inflicted gunshot wound to the head.

Authorities found multiple registered and unregistered guns at Berhow’s Santa Clarita home. Six of the guns were registered to his late father and several more were unregistered, along with the pistol used in the killings.

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Authorities still have no motive in the shootings. The victims appear to have been targeted at random.

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Saugus High School will remain closed through Thanksgiving break and will not reopen until Dec. 2.