A childhood friend of the man accused of shooting dead nine people inside a black church in South Carolina said he told him a few weeks ago he had "a plan".
Joey Meek, who alerted the FBI after recognising Dylann Roof in a surveillance camera image, said he was drinking vodka with him when he made the remark while he was railing against blacks.
Roof (21) did not elaborate, but Mr Meek said he was worried and knew his friend had a .45 calibre Glock pistol in the boot of his car, which Roof told him he bought using birthday money from his parents.
Because of the way Roof was behaving, Mr Meek said he took the gun from the car and hid it in his house, just in case.
"I didn't think he would do anything," he said. But the next day, when Roof was sober, he gave it back.
Mr Meek's brother, Jacob, said he recalled that as they were driving to a lake on Wednesday, the day of the Charleston church massacre, Roof said he should be careful moving his backpack in the car because of the "magazines".
But Jacob Meek thought Roof was referring to periodicals - instead of a device that stores ammunition.
"Now it all makes sense," he said.
Joey Meek said they had been best friends in middle school, then lost touch for years until Roof reappeared a few weeks ago.
"All the sudden out of the blue, he started talking about race. He started talking about (black Florida teenager killed by a neighbourhood watch volunteer) Trayvon Martin," Mr Meek said.
"He said blacks were taking over the world. Someone needed to do something about it for the white race. He said he wanted segregation between whites and blacks. I said, 'That's not the way it should be'. But he kept talking about it."
Roof, said to have joined a prayer meeting inside the historic church before the murders, has been returned to South Carolina after being captured without resistance in neighbouring North Carolina.
He is being held at a detention centre pending a bail hearing.
Roof had a criminal record, and court records show a pending misdemeanour drug case and a past misdemeanour trespassing charge.
He proudly displayed the flags of defeated white-ruled regimes, posing with a Confederate flag plate on his car and wearing a jacket with stitched-on flag patches from Rhodesia, which is now black-led Zimbabwe, and apartheid-era South Africa.
He spent nearly an hour inside The Emanuel African Methodist Episcopal Church in Charleston on Wednesday night before killing six women and three men, including the pastor, state senator Clementa Pinckney.
Stunned community leaders and politicians condemned the attack and US attorney general Loretta Lynch said the Justice Department had begun a hate crime investigation.
President Barack Obama, who personally knew the murdered pastor, said such shootings had to stop.
"At some point, we as a country will have to reckon with the fact that this type of mass violence does not happen in other advanced countries," he said.