Dalton Tyler, who said he has known Roof for seven months to one year, said he saw the white, 21-year-old suspect just last week.
“He was big into segregation and other stuff,” Tyler said. “He said he wanted to start a civil war. He said he was going to do something like that and then kill himself.”
Tyler said he met Roof, a Lexington, South Carolina native, through a good friend. He also said Roof’s parents, with whom he said the suspect was “on and off,” had previously bought him a gun but never allowed him to take it with him until this past week.
Dylan Roof’s grandfather, Joe Roof, declined to comment to ABC News.
Police said Roof was arrested today at a traffic stop in Shelby, North Carolina, about 250 miles north of Charleston.
A citizen saw the suspect’s car and reported it to police, who responded and made the arrest, police said. Roof cooperated with the officer who stopped him, according to police.
Officials said they believe Roof acted alone.
"I am so pleased we were able to resolve this case quickly," Charleston Police Chief Gregory Mullen said at a news conference.
A court clerk confirmed to ABC News this afternoon that Roof waived extradition in North Carolina and is cleared to return to South Carolina.
ABC News' Cleopatra Andreadis contributed to this report.