Jaleyn Saulsberry, 19, is charged with one count of first degree murder and three counts of issuance of warrant. Saulsberry was initially arrested on a different warrant in Pennsylvania and held on a $2 million murder warrant.
He was extradited to Chicago and is due in bond court Friday morning.
Brown did not immediately identify the individual.
Devin Barron, 20, of Lynwood, Dwain Johnson, 18, and a 15-year-old boy who has not been identified by name have also been charged in the shooting.
WATCH: Raw surveillance video of attempted carjacking, shooting
CPD release surveillance video of Morgan Park shooting that killed retired Chicago firefighter
Williams, a beloved retired CFD lieutenant, was walking out of a popcorn shop in Morgan Park at 117th Street and Western Avenue on Dec. 3. Surveillance video captured the shooting exchange with Williams and the group trying to approach him. Williams was hit and later died.
Mayor Lightfoot, Chicago police discuss charges in firefighter's death
Chicago police, Mayor Lightfoot speak after boy charged in shooting of retired firefighter
Williams, 65, spent 28 years with the Chicago Fire Department and later worked at OEMC specializing in coordinating the city's surveillance cameras.