Chris Harper-Mercer

Following the shooting, Bureau of Alcohol, Tobacco, Firearms and Explosives (ATF) agents launched a campus-wide search for explosives. Six firearms were recovered from the crime scene: five handguns and one long gun. None were owned by his mother. The long gun, a 5.56x45mm Del-Ton DTI-15 semi-automatic rifle, was not used during the incident. Harper-Mercer also had a flak jacket and "enough ammunition for a prolonged gunfight". Police said they found eight other firearms at his apartment, and that all of the weapons were purchased legally by him or members of his family. Almost four hours after the shooting, Laurel Mercer was interviewed by Oregon State Police detectives, but the content was not released until September 13, 2017. She said her son had been prescribed medication, but it didn't seem to help, and that he had been "born angry." She told police that he enjoyed watching videos of killings on the Internet. Their home was so disordered, that after the murders, she couldn't tell what guns were missing.

Although Harper-Mercer had suffered from substantial mental illness, he had never been involuntarily committed (which under federal and state law prohibits a person from purchasing a gun). Harper-Mercer was therefore able to pass a background check and bought a .380 semiautomatic handgun. An Oregon law passed in 2017, which went into effect in 2018, allows law enforcement or family members to file a petition in state court for an "extreme risk protection order"; such an order, if granted, temporarily blocks an individual from purchasing or possessing deadly weapons if the individual is determined to present an "imminent threat to themselves or others." Had the law been in effect earlier, it is possible that Harper-Mercer could have been prevented from purchasing his weapon.

A memorial for the victims of the shooting was unveiled in December 2016.

The Umpqua Community College shooting occurred on October 1, 2015, at the UCC campus near Roseburg, Oregon, United States. Chris Harper-Mercer, a 26-year-old student who was enrolled at the school, fatally shot an assistant professor and eight students in a classroom. Eight others were injured. Roseburg police detectives responding to the incident engaged Harper-Mercer in a brief shootout. After being wounded, he killed himself by shooting himself in the head. The mass shooting was the deadliest in Oregon's modern history.

On the day of the shooting, Harper-Mercer gave a survivor numerous writings showing he had studied mass killings, including the 2014 killing spree at Isla Vista, California. These expressed his sexual frustration as a virgin, animosity toward black men, and a lack of fulfillment in his isolated life. In them, he said "Other people think I'm crazy, but I'm not. I'm the sane one," and that he would be "welcomed in Hell and embraced by the devil." He also reportedly admired the perpetrator of the WDBJ shooting for the fame received, and wrote that: "A man who was known by no one, is now known by everyone. His face splashed across every screen, his name across the lips of every person on the planet, all in the course of one day."

He and his mother moved to Winchester, Oregon in 2013 after she received a job there. His mother said he was initially excited to be able, unlike as in California, to be permitted to "open carry." There were fourteen legally purchased weapons kept in the apartment, and Harper-Mercer's mother wrote online that she always kept full magazines in Glock pistols and an AR-15 rifle inside. The two often spent time together at shooting ranges, but Harper-Mercer was otherwise extremely isolated.

Harper-Mercer maintained several Internet accounts, including one in which he described himself as mixed race. Media reports said he had an e-mail address linked to an account on a BitTorrent website. The last upload on the account, three days before the Umpqua shooting, was a documentary on the 2012 Sandy Hook Elementary School shooting. According to the date of the post, he made an announcement post on 4chan's /r9k/ board possessing the message "Some of you guys are alright. Don't go to school tomorrow if you're in the northwest. Happening thread will be posted tomorrow. See you later space robots". According to the Los Angeles Times, unnamed law enforcement sources described him as a "hate-filled" man with antireligious and white supremacist leanings, and with long-term mental-health issues. His mother, Laurel Harper, had previously written anonymously in an online forum that both she and her son had Asperger syndrome.

Harper-Mercer joined the U.S. Army in 2008, but was discharged after five weeks for his failure to meet the "minimum administrative standards" of basic training at Fort Jackson, South Carolina. Officials linked to the investigation said that he was discharged as the result of a suicide attempt, but Army officials did not comment on this. In 2009, he graduated from Switzer Learning Center, a school for teenagers with learning disabilities or emotional issues. Laurel Harper was reportedly protective of him and tried to shield him from various perceived annoyances, some of them minor, in their neighborhood in Torrance. From early 2010 to early 2012, Harper-Mercer attended El Camino College in Torrance.

Christopher Sean "Chris" Harper-Mercer (July 26, 1989 – October 1, 2015) was enrolled in the introductory composition class where he shot his victims. He was born in Torrance, California to Ian Mercer and Laurel Margaret Harper, and lived with his mother during the separation and divorce of his parents, who agreed to shared legal custody. Harper-Mercer continued to live with his mother and remained with her when she moved to Oregon for work. His father had not seen him for about two years following his son's move out of state.