In disturbing images posted online, Harper-Mercer, who was born in England and moved to the States at a young age, posed with guns and shared pro-IRA newspaper front pages, an Express.co.uk investigation has found.
He also posted a three-minute video on the social networking site MySpace featuring IRA fighters branding guns and wearing balaclavas.
On his dating profile on the website Spiritual Passions, he wrote that he “doesn’t like organised religion”.
Chris Harper-Mercer appeared to buy Nazi memorabilia online
“i will continue to make purchases from this company. i am very impressed with there products/service and highly recommend them. thanks Steve”
Harper-Mercer on the day of his brother’s wedding
Harper-Mercer listed himself as spiritual but non-religious
He was armed with three handguns and an AR-15-style long gun, and was killed after a shootout with police on the scene yesterday, according to reports.
He worked on a Noel Coward play by the school’s drama group
Harper Mercer also said he was “mixed race”, did not drink and was a “conservative, Republican”.
WATCH: THE IRA VIDEO POSTED ON HARPER-MERCER’S MYSPACE PAGE
He shared this newspaper front page on MySpace
“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.
“Seems the more people you kill, the more your’re [sic] in the limelight.”
The most recent torrent uploaded by the account username was a BBC documentary about the aftermath of the Sandy Hook shooting, according to Gawker.
Hours before the attack, an anonymous poster on the message board 4Chan, warned: “Some of you guys are alright. Don’t go to school tomorrow if you are in the northwest.”
Oregon is a state in the Pacific northwest of the United States.
Another post read: “Happening thread will be posted tomorrow morning. So long space robots. Will post again am. 10 min countdown. Won’t say more to much to prepare.”
Harper-Mercer’s devastated family have reacted to the news, saying they are “shocked”.
Close to tears, his father said: “I am just as shocked as everybody about what happened today.
“i can’t answer any questions right now and I don’t want to answer any questions right now. Obviosuly it’s devastating for me and my family.”
His step-sister said: “I am still in shock. All he ever did was put everyone before himself.
“He wanted everyone to be happy, no matter if he was sad or mad he would always try to cheer up everybody.”
Clearly distressed and with her head in her hands, she added: “It doesn’t sound like something he would go through.”