Oregon college gunman Chris Harper Mercer has been described as an "uncommunicative" loner who was ejected from the US Army after less than a month of service.
Reportedly born in the UK, the 26-year-old lived with his mother a few miles away from Umpqua Community College, where he opened fire on Thursday morning, killing nine people before dying in a police shootout.
His father and stepsister were shocked by the shooting and a neighbour said his mother could be heard late on Thursday "crying her eyes out" in the family's apartment.
"All he ever did was put everyone before himself, he wanted everyone to be happy," said Carmen Nesnick, his stepsister.
But former neighbours in Oregon and California said Mercer hardly spoke and "seemed really unfriendly".
He enlisted in the Army in 2008, but he was discharged after spending less than a month in basic training, a US Army spokeswoman told the BBC.
She did not disclose why he was discharged, citing privacy rules.
Police think Mercer may have been a student at Umpqua because he was found with a receipt from the campus bookstore showing he had purchased textbooks.
Mercer is not believed to have a criminal history allowing him to legally own a large cache of weapons. He is shown posing with a rifle in a photograph posted online.
Police said he was wearing metal-plated body armour when he was killed.
It appeared that Mercer had posted information about himself on a MySpace page and an online dating profile.
His MySpace page contained pictures of masked gunmen, a picture of the front page of the Irish republican newspaper An Phoblacht carrying the headline "British Army Could Not Defeat IRA" and a photograph with the words "IRA undefeated army".
In a dating profile apparently belonging to Mercer on the Spiritual Passions website under the username Ironcross45, the non-smoking teetotaller described himself as "shy at first, but [I] warm up quickly, better in small groups".
He listed hobbies including the internet and "killing zombies", described his politics as "conservative, republican" and said he was spiritual but not religious.
Ms Nesnick said Mercer was born in the UK and moved to the US as a young boy.
Before moving to Oregon, Mercer and his mother lived for several years in a housing complex in the Los Angeles suburb of Torrance.
One neighbour, David Westly, said Mercer had told him his mother went shooting at a range and added that he had seen Mercer and his mother leaving and returning to the apartment with what looked like gun cases.
A local newspaper in Torrance, the Daily Breeze, claimed that Mercer had attended a school for teenagers with behavioural problems.
The paper said its own published lists of graduating students showed Mercer attended a school called the Switzer Center, which specialises in teaching students with special needs and behavioural issues.