Investigators with the Federal Motor Carrier Safety Administration have been at Ricky Lucas Trucking in Roseboro.
Authorities say the driver, Johnny Spell, passed a stopped school bus on Tuesday, and hit and killed Alyiah Morgan as she was crossing U.S. Highway 421.
Authorities say Spell did not stop following the accident and he and the truck were found two hours later near Roseboro.
Spell remains in jail. He's charged with DWI and involuntary manslaughter.