Federal and local authorities have found that the man charged in the shooting deaths of nine black people in a South Carolina church last month had been in contact with white supremacists online, although it does not appear they encouraged him to carry out the massacre, according to law enforcement officials. Investigators uncovered that information as they have pieced together where the gunman, Dylann Roof, 21, received his inspiration, and whether anyone else should face charges in connection with the murders. “To understand what happened, you have to understand who he talked to and who may have known what,” said one law enforcement official briefed on the case. The officials spoke on the condition of anonymity because they did not want to be identified discussing a continuing investigation.