A website has surfaced with the alleged racist writing, and a series of photographs that appear to show Dylann Roof, the suspect in the deadly church shooting in the US state of South Carolina.
The authenticity of the website, which surfaced on Saturday, or who created it, could not be immediately confirmed. But Al Jazeera Gabriel Elizondo, who is reporting from the city of Charleston, has confirmed that it was registered by Roof.
Al Jazeera has also spoken to Roof's father, but he would not confirm that his son created the site.
In the website, the author provides a cryptic "explanation," for action, saying, "I have no choice ... I chose Charleston because it is most historic city in my state, and at one time had the highest ratio of blacks to Whites in the country.
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It also shows a photo of the suspect carrying a gun and a controversial flag, seen as a symbol of racism in the United States.
The FBI said it was reviewing the manifesto purportedly written by the suspected gunman, Associated Press reported.
A federal law enforcement official close to the investigation said the FBI is aware of the website and is reviewing it. The official spoke on condition of anonymity because he was not authorised to speak publicly on the case.
The website surfaced as mourners arrived in the city of Charleston from around the US on Saturday, to pay their respects to the nine African American victims.
Services were planned throughout the day ahead of a rally in South Carolina's state capital, Columbia, later in the evening.
Roof, a 21-year old white man, was arrested on Thursday and charged with nine counts of murder and a weapons charge for the fatal shooting at the Emanuel African Methodist Church in Charleston.
A police affidavit released on Friday accused Roof of shooting all nine multiple times, and making a "racially inflammatory statement" as he stood over an unidentified survivor.
Authorities said he spent an hour in Bible study with parishioners at the historically black church before opening fire on them on Wednesday evening.
"We are told to accept what is happening to us because of ancestors wrong doing, but it is all based on historical lies, exaggerations and myths," the author writes in the text of the site.
Charleston was an important port city during the American Civil War in the 1860's, pitting the breakaway pro-slavery southern US states, against the rest of the country under the control of the federal government.
Crowds began to gather at the Emanuel African Methodist Church early on Saturday.
At the memorial site in front of the church, the oldest African-American congregation in the southern US, flowers were laid two metres deep in places.
Placards and signs offered words of solace and prayer but also frustration at another act of gun violence.
A black T-shirt hung on the church gate had white lettering that read: "Do you believe us now? Change must come."
Monte Talmadge, a 63-year-old US Navy veteran, drove nearly 480 km overnight from Raleigh, North Carolina, and sat in a camping chair across the street from the church.
The bloodshed in Charleston is the latest in a series of fatal mass shootings in the US.
The violence has renewed a national debate on tighter controls on gun possession, as well as racial discrimination against African Americans in the country.
Activists were calling for the removal of the Confederate battle flag from the grounds of the state house because of what some people see as its racist associations.