Delaware's Department of Justice says John Wallace-Bey is being held on a $3 million cash bail.
His arraignment is scheduled for July 14.
RELATED: Community holds vigil for victims of Wilmington Hospital shooting
Wallace-Bey was arrested in Philadelphia after the shooting on June 16.
Ethan Hillman, 19, was killed, and another 19-year-old man was injured.
There has been no word on a motive for the shooting.