FERGUSON, Mo. -- Desiree Harris saw her grandson running near her home Saturday afternoon when she passed him in her car. Minutes later, she found his body on the street -- fatally shot by a police officer.

The shooting of the black teenager, a recent high school graduate, sent hundreds of angry residents out of their apartments in the predominantly black St. Louis suburb of Ferguson in a confrontation with police that lasted several hours. They shouted obscenities and some threats, such as "kill the police," but there were no reports of additional injuries.

Harris said she was expecting her 18-year-old grandson, Michael Brown, to visit her that afternoon and discovered him dead after she heard the commotion outside the apartment complex.

"He was running this way," she said. "When I got up there, my grandson was lying on the pavement. I asked the police what happened. They didn't tell me nothing."

Officer Brian Schellman, spokesman for the St. Louis County Police Department, said "a couple hundred" people came out of apartment buildings after an officer with the Ferguson Police Department shot and killed the male. Schellman did not identify the person who was shot or say what prompted the shooting.

John Gaskin, a member of the St. Louis County NAACP, called on the FBI's assistance was needed "to protect the integrity of the investigation."

"With the recent events of a young man killed by the police in New York City and with Trayvon Martin and with all the other African-American young men that have been killed by police officers ... this is a dire concern to the NAACP, especially our local organization," Gaskin said.