Dylann Roof, the suspect in Wednesday's church massacre in Charleston, appears to have written a racist manifesto, posed in photographs with a handgun, and stood in front of a Confederate military museum and plantation slave houses.
The photos and text surfaced on a website on Saturday. Reuters could not immediately confirm who created the website or the authenticity of the photographs posted on it.
Investigators were aware of the postings and taking steps to verify their authenticity, the FBI said in a statement.
Many of the local landmarks shown in the photos appeared chosen to highlight Charleston's segregated past and to touch a nerve with the city's black community by singling out sites with a special importance and sensitivity in African-American history.
Roof, a 21-year-old white man, was arrested on Thursday and charged with the murders of nine African-Americans at the Emanuel African Methodist Church in downtown Charleston. Authorities say he spent an hour in an evening Bible study group at the historically black church before opening fire on the parishioners.
The text posted on the site outlines the author's view of the superiority of white people and says they have no reason to feel guilt about the treatment of African-Americans. The author provides an "explanation" for taking some unspecified action.
"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."
Among the photos on the site are a close-up of a .45 caliber handgun, the same type of weapon that police say was used to carry out the church shootings.
Other images show a young man who strongly resembles Roof. One shows the man holding the handgun and a small Confederate flag. He is also pictured on a beach crouching by white supremacist symbols scrawled in the sand.
The website surfaced as mourners arrived in Charleston from around the United States on Saturday to pay their respects to those killed. Services were planned throughout the day ahead of a rally in Columbia, the state capital, later in the evening.
The massacre was the latest in the series of bloody mass shootings in the United State that have reignited a debate over gun control in a country where the right to own firearms is constitutionally protected.
President Barack Obama has called for gun law reforms, and in extracts of an interview posted on Saturday he blamed public apathy and what he called a tight "grip" on Congress of the National Rifle Association, the powerful US gun lobby, for blocking stricter laws.
The killings were shattering to a city steeped in history. Charleston was an important port city during the American Civil War in the 1860's, pitting the breakaway Confederate states against the Union Army under the control of the US federal government.
The main issue dividing the country was slavery, with the rebel Southern states insisting on their right to decide for themselves whether to allow a practice they saw as vital to their plantation economy.
Dylan Roof appearing on trial via camera, attacked a black church in Charleston, in an act motivated by racism.
Crowds gather outside church
The Emanuel African Methodist Church will reopen for worship on Sunday, Reverend Ronnie Brailsford, pastor of the Bethel African Methodist Church in Columbia said on Saturday. Church officials in Charleston could not be reached for comment.
Crowds gathered outside the church from early on Saturday. At the memorial site in front of the church, the oldest African-American congregation in the southern United States, flowers were laid six feet (two meters) deep in places.
Placards and signs offered words of solace and prayer but also frustration at another act of gun violence.
Monte Talmadge, a 63-year-old US Navy veteran, drove nearly 300 miles (480 km) overnight from Raleigh, North Carolina, and sat in a camping chair across the street from the church.
"There was an overwhelming feeling that made me drive here," he said. "A church is a place of worship, not a place for killing."
At a weekly farmers market in Charleston's Marion Square park, a few hundred yards (meters) from the church, residents sat shaded from the sun to eat lunch. Live music was played from a stage. Earlier a group of about 75 people gathered to for gospel singing and prayer in the park.
At Wragg Mall in Charleston later on Saturday evening, a few hundred people gathered at a park to march down to the Emanuel church a few blocks away. Many were dressed in black and carried flowers to lay in front of the church.
Residents from across the area were expected to gather in the early evening on the Ravanel Bridge, one of Charleston's main thoroughfares, connecting the city with Mount Pleasant across the Cooper River. Local organizers hoped some 3,000 people would join hands along the bridge's footpath.
The first demonstration since the shooting was scheduled for 6pm in Columbia. 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.
The flag was removed from the roof of the state house in 2000 and placed on a monument to the confederate soldier near the legislature. Calls were growing for its removal.