The officer who shot the 18-year-old has been with the Ferguson Police Department for six years, and has not had any other issues since he has been on the force, Belmar said. His name has not been disclosed.
He will be interviewed extensively today and will have a physiological evaluation before returning to duty, the chief said. The officer is currently on paid administrative leave.
Jackson told The Associated Press that police have contacted the second person who was involved in the altercation with the officer before the shooting, but that the person has not been arrested or charged.
The local chapter of the NAACP has called for the FBI to handle the investigation of the shooting. Belmar said that the FBI could become involved, but had not as of today.
State Sen. Jamilah Nasheed, D-St. Louis, told the St. Louis Post-Dispatch she would ask the U.S. Justice Department on Monday for a formal investigation.
ABC News' Rachel Katz and The Associated Press contributed to this report.