The weapon used in the Saugus High shooting one week ago was determined to be a “kit gun,” officials said Thursday.

As the investigation continues into the Saugus High shooting, investigators have determined the .45 caliber pistol used was a kit gun, said Los Angeles County Sheriff Alex Villanueva.

“The weapon used in the homicide was a kit gun, it was assembled from parts and had no serial number,” Villanueva said.

A student opened fire with the kit gun in the Saugus High School quad, killing two classmates and himself, according to Sheriff’s officials.

Multiple other students were injured in the Saugus High shooting, officials said.

The suspect grew up in a house where his father had weapons, according to officials.

“The father had six guns registered to him,” Villanueva said.

See Related: Final Survivor Of Saugus High Shooting Released From Hospital

However, at one point all the weapons were lawfully removed from the home and legally destroyed, according to officials.

After the shooting occurred, a search warrant was issued at the suspect’s home, and investigators found additional firearms in the house which were also discovered to be kit guns, Villanueva said.

The Saugus High shooting is still under active investigation, and “the ‘why’ is still a mystery,” Villanueva said.

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