CHARLESTON, SC (CNN) -- When church shooting suspect Dylann Storm Roof turned 21 in April, his father bought him a .45-caliber gun, a senior law enforcement source briefed on the investigation said Thursday.
It's not known whether that handgun was used when Roof allegedly opened fire Wednesday night at a prayer meeting at Emanuel African Methodist Episcopal Church in Charleston, South Carolina, killing nine people.
"You rape our women and you're taking over our country. And you have to go," Sylvia Johnson, a cousin of the church's slain pastor, said the gunman told his victims, according to CNN affiliate WIS. She cited survivors of the shooting.
The suspect, who is white and slightly built, was at the historic African-American church for about an hour, attending a meeting with his eventual victims, before the massacre, according to Charleston police Chief Greg Mullen.
U.S. Sen. Lindsey Graham, R-South Carolina, said his niece, Emily, was in an eighth-grade English class with Roof.
"He was quiet, strange, very unsocial and everyone thought he was on drugs," Graham, a U.S. senator from South Carolina, said of the suspect, relaying the description from his niece Emily and sister Darline Graham Nordone.
The niece did not recall Roof making statements related to race, Graham said.
"I just think he was one of these whacked-out kids. I don't think it's anything broader than that," said Graham, who is running for president. "It's about a young man who is obviously twisted."
Witnesses told investigators the gunman stood up and said he was there "to shoot black people," a law enforcement official said.
The victims "were killed because they were black," Charleston police spokesman Charles Francis told CNN on Thursday. Francis was asked what led authorities to investigate the shooting as a hate crime.
Investigators are looking into whether Roof had links to white supremacist or other hate groups, a law enforcement official said. There is no indication so far that he was known to law enforcement officials who focus on hate groups.
In an image tweeted by authorities in Berkeley County, South Carolina, Roof seen is wearing a jacket with what appear to be the flags of apartheid-era South Africa and nearby Rhodesia, a former British colony that a white minority ruled until it became independent in 1980 and changed its name to Zimbabwe.
Roof was armed when he was arrested Thursday in Shelby, North Carolina -- about a 3½-hour drive north-northwest of Emanuel AME Church, according to a law enforcement official briefed on the investigation. It's not clear if it's the same firearm used in the shootings.
Police had earlier said that Roof, of Lexington, South Carolina, may have been driving a black Hyundai with vehicle tag LGF330. He was arrested after a traffic stop prompted by a tip from a citizen, police said.
A mug shot of Roof from Lexington County was released Thursday. It was taken after a trespassing arrest in April. According to an arrest warrant from a February incident, Roof had an unlabeled pill bottle with a drug believed to be suboxone, which is used to treat opiate addiction. Roof told police a friend gave him the drugs. The status of the cases is unclear.
Police released a flier Thursday morning with details of the suspect as they appealed for help to identify and track him down.
Charleston Police Chief Gregory Mullen told a news conference that officers "have obtained surveillance videos of the suspect in this case and a suspect vehicle."
Mullen said the suspect was a "younger white male between 21 and 25 years of age, 5-foot-9 in height" and "has a very distinctive sweatshirt that has markings."
Mullen emphasized the suspect is "a very dangerous individual."
Woman spared by shooter to give account?
A female survivor told family members that the gunman told her he was letting her live to tell everyone else what happened, Dot Scott, president of the local branch of the NAACP, told CNN.
Scott said she had not spoken to the survivor directly but had heard this account repeated at least a dozen times as she met with relatives of the victims Wednesday night. Scott added that she didn't know if the survivor had ended up at the hospital or being questioned by police.
Because of the church's historic significance, it is not unusual for visitors, whether white or black, to visit it, Scott said. She said she'd had no indication that any children were among the victims.
Mullen told the news conference the suspect had been in the church attending a meeting that was going on -- and "stayed there almost an hour with the group before the actual event."
But he declined to comment on whether the suspect had let one woman escape.
'Distinctive' license plate
The suspect was seen leaving the church in a black four-door sedan, the flier says. "The vehicle you will see has a very distinctive front license plate," Mullen added, but did not give further details on what made it stand out.
He appealed for the media to help in circulating the suspect's image and for the public to be vigilant. The clean-shaven man pictured wears a gray sweatshirt over a white T-shirt, blue jeans and Timberland boots.
Police are "going through all kinds of video" and trying to identify any private or public video that may show anything useful for the investigation, Mullen said.
"No one in this community will ever forget this night and as a result of this and because of the pain and the hurt this individual has caused this entire community, the law enforcement agents are committed and we will catch this individual," he said.
Charleston Mayor Joe Riley described the suspect as "somebody filled with hate and with a deranged mind."
The man is a "no-good, horrible person," he said. "Of course we will make sure he pays the price for this horrible act."
Six of those killed in Wednesday night's attack at the Emanuel African Methodist Episcopal Church were female and three male. The victims included the church's pastor, the Rev. Clementa Pinckney.
A statement from the Georgia branch of the NAACP said, "There is no greater coward than a criminal who enters a house of God and slaughters innocent people engaged in the study of scripture."
CNN's AnneClaire Stapleton and Deborah Feyerick contributed to this report.
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