Cho Seung-hui, who staged America's worst shooting massacre, has revealed himself as a deeply disturbed individual, obsessed with violence and harbouring profound and unexplained grievances, apparently against his fellow students.
Cho said he had been forced into a corner
In his series of videos and still photos broadcast days after the shootings, he was seen brandishing weapons and ranting angrily against "brats", snobs" and "rich kids", who he said had "raped his soul" and forced him to do what he did.
He also appears to pay homage to the perpetrators of previous massacres, in particular the "martyrs" of Columbine High, and his poses with guns are eerily reminiscent of those of his apparent heroes.
He compares himself to Jesus Christ, inspiring "generations of the weak and the defenceless people".
Psychologists say the footage indicates he could have been suffering from a severe case of grandiosity and possibly either bipolar depression or schizophrenia.
The package is immensely long, rambling and full of profanities, consisting in total of an 1,800-word diatribe, 43 photos and 28 video clips. It is thought he may have been planning the attack for more than a month.
His diatribes may have come as a shock to many of his peers, who have described him as a quiet and unassuming loner - though many were aware of his violent side.
Several members of staff have referred to his creative writing, which they said was so disturbing that he was referred to counselling.
The professor who taught him, Lucinda Roy, said she spoke repeatedly to the
university authorities about him, adding she was so concerned by what she found that she decided to take him out of the classroom for one-to-one tutoring.
Immigration records show that Cho was born in South Korea on 18 January 1984 and had moved to the US in 1992, when he was eight.
South Korean media said his family was very poor and lived in a cheap rented basement apartment in the northern Changdong district of the capital Seoul. They decided to emigrate to seek a better life, although they had no acquaintances in the US.
Cho lived in the US with his family from the age of eight
The landlord of the apartment was quoted as saying that Cho was "very quiet and well-behaved".
"I don't believe he did it," she said, quoted by Yonhap news agency.
In the US, his parents set up a dry-cleaning business. They live in Fairfax County, an affluent suburb of Washington DC, just outside Arlington and Alexandria.
His sister graduated from the elite Princeton University.
Cho had resident alien status, and had last renewed his green card in October 2003. However he is thought to have also retained his South Korean citizenship.
'One word answers'
Cho lived on the university campus, in a dormitory called Harper Hall.
He was in the final year of an English degree and kept a low profile at home, rarely speaking to those with whom he shared a three-room flat.
"He was just a very anti-social sort who was very quiet and never talked at all," roommate Joseph Aust told the BBC.
"I tried to make conversation with him but he would give one word answers. Other times he would just ignore me."
"I did feel that he was a bit lonely 'cos I never saw him hanging with anybody," said Karan Grewal, another roommate.
"I figured he was pretty lonely, but not that he was angry in any way or he was capable of what he did."
However, it was later revealed by police that he had been admitted to a mental health unit in late 2005, after complaints made against him by two female students.
There were reports that he had shown recent signs of violent behaviour, including starting a fire in a dormitory, and that he may have taken medication for depression.
Cap and sunglasses
Neighbour Abdul Shash described Cho as "very quiet, always by himself", and said he spent a lot of time playing basketball and would not respond if someone greeted him.
Ms Roy told ABC News that Cho seemed "extraordinarily lonely - the loneliest person I have ever met in my life".
She described how he wore sunglasses indoors and a cap pulled over his eyes, adding that he spoke in a whisper, paused before answering questions and took mobile phone pictures of her in class.
"I was so uncomfortable that I didn't feel that I could leave him in the classroom," she told CNN.
Fellow student Julie Poole said that on the first day of a literature class last year the students introduced themselves one by one, but when it was Cho's turn, he did not speak.
The professor, she said, looked at the sign-in sheet and where everyone else had written their names, Cho had written a question mark.
"We just really knew him as the question mark kid," Ms Poole added.