The man armed with several guns who walked into a Thursday morning writing class at a rural Oregon community college and fatally shot nine people, died of an apparent self-inflicted gunshot wound.
Douglas County Sheriff John Hanlin, speaking at a news conference Saturday, said the medical examiner's office has determined the cause of death as suicide.
Officials initially said the shooter, identified as 26-year-old Christopher Harper-Mercer, was killed during a shoot out with officers responding to the Umpqua Community College campus. The worst mass shooting in Oregon history also injured nine people.
Hanlin also revealed an additional gun was found at the apartment Harper-Mercer shared with his mother, bringing the total number of weapons seized to 14.
Harper-Mercer was armed with a 9mm Glock pistol and .40-caliber Smith & Wesson, according to a Bureau of Alcohol, Tobacco, Firearms and Explosives incident report obtained by The Associated Press.
Mercer also had a .40-caliber Taurus pistol traced to someone in Portland and a .556-caliber Del-Ton.
ATF Assistant Special Agent in Charge Celine Nunez announced Friday at a news conference that six weapons were recovered at the college campus and an additional seven were found at the shooter's home.
Nunez said the firearms were purchased legally by the shooter or a family member in the last three years. Officials did not say whether the latest gun found at Harper-Mercer's home was purchased legally.
Investigators also found a flak jacket next to a rifle at the school, which contained steel plates, Nunez said.
Officials conducting searches at the school, shooter's residence and vehicle have also seized documents and digital media, Hanlin said.
"The Oregon State Police Crime Lab as well as the ATF and FBI Laboratories are all engaged in the effort to move forward with processing this evidence," he added.
Douglas County District Attorney Rick Wesenberg said the Oregon State Police's investigation into the officer-involved shooting is "nearing conclusion."
"I expect to be presented with the case early next week. Once I receive the case, I will do a thorough review and make a determination on whether the use of force was justified," he said.
In a statement, Harper-Mercer's family expressed their grief and offered prayers to the families of the victims.
"We are shocked and deeply saddened by the horrific events that unfolded on Thursday, October 1. Our thoughts, our hearts and our prayers go out to all of the families of those who died and were injured," the statement read.
Law enforcement officials told NBC News that Mercer left behind a multi-page document at the shooting scene espousing what one of them called "a philosophy of hate."
Two officials familiar with the contents say he wrote that he would be "welcomed in Hell and embraced by the devil."
The officials said he lamented the fact that he had no girlfriend. "He said he had no life," another official said, adding, "He felt the world was against him."