The gunman who killed nine in a mass shooting at an Oregon community college killed himself as officers arrived, according to officials.

"The medical examiner has determined the cause of death of the shooter to be suicide," Douglas County Sheriff John Hanlin told reporters at a press conference on Saturday, according to NBC News. Hanlin added that the investigation was ongoing, and that authorities had recovered an additional handgun from the home of Chris Harper Mercer, bringing the total to 14 guns owned by the gunman that authorities have seized.

On Thursday morning, the 26-year-old Mercer opened fire in a class that he was enrolled in at Umpqua Community College in Roseburg, Oregon. In the end, Mercer killed nine people, identified by officials as Lucero Alcaraz, 19; Quinn Glen Cooper, 18; Kim Saltmarsh Dietz, 59; Lucas Eibel, 18; Jason Dale Johnson, 33; Lawrence Levine, 67; Sarena Dawn Moore, 44; Treven Taylor Anspach, 20; and Rebecka Ann Carnes, 18. An additional 9 people were wounded.

At the press conference today, officials say officers arrived six minutes after the first 911 call, and responding officers exchanged fire with Mercer two minutes after they arrived. Two minutes later, Mercer was said to be down.

Officials also revealed that a "manifesto" was uncovered at the scene and left as a message to law enforcement, according to the AP, but did not say what the document contained. A source told NBC News that Mercer wrote that he "felt the world was against him" and that his actions would allow him to be "welcomed in Hell and embraced by the devil." Initial reports said Mercer specifically targeted Christians in his attack, but the mother of one of the wounded victims, say the gunman only asked if his victims were religious, without specifying Christianity.