The African-American man suspected of killing two US journalists was a disgruntled former employee of their TV station who claimed to be motivated by racism.
Vester Lee Flanagan, also known as Bryce Williams, was formerly a reporter at Virginia state TV station WDBJ.
Hours after he allegedly shot dead reporter Alison Parker, 24, and her cameraman Adam Ward, 27, at close range during an on-air interview, he contacted US station ABC News and claimed he was pushed over the edge by the recent massacre of African-Americans in South Carolina.
ABC News said it received a rambling 23-page manifesto two hours after Ms Parker and Mr Ward were killed on Wednesday as they were conducting a live interview near Roanoke, Virginia.
“The church shooting was the tipping point … but my anger has been building steadily … I’ve been a human powder keg for a while … just waiting to go BOOM!” Flanagan allegedly wrote.
The suspect was found in his car on Wednesday with a self-inflicted gunshot wound. He later died in hospital.
The statement’s author identified himself in the document as Bryce Williams, and a man who called ABC News at 10am introduced himself as Bryce and said he had shot two people that morning.
He said authorities were “after me” and “all over the place” before hanging up, ABC said.
In the document labelled a “Suicide Note for Friends and Family,” the author complained of racial discrimination and bullying “for being a gay, black man”.
But he said the church shooting in Charleston, South Carolina was what drove him to commit Wednesday’s murders.
“Why did I do it? I put down a deposit for a gun on 6/19/15. The Church shooting in Charleston happened on 6/17/15 …
“What sent me over the top was the church shooting. And my hollow point bullets have the victims’ initials on them.”
ABC News said he also expressed admiration for the perpetrators of the 1999 Columbine High School massacre and said he was influenced by Seung-Hui Cho, the student who carried out a mass killing at Virginia Tech University in April 2007.
Investigators in Virginia said on Wednesday they were examining the manifesto.
The incident has renewed calls in the US for tighter gun control.