Johnthony Walker was also using his cell during the bus route, which is prohibited, a police investigator testified.
The Tennessee school bus driver in a deadly crash that killed six children was speeding when he swerved off a road and slammed into a tree, a police investigator testified Thursday.
Johnthony Walker, 24, was also using his cell phone during his route, but Chattanooga Police Department Officer Joe Warren did not say when that happened, CBS affiliate WTVR-TV reported.
Read: Driver Accused in Chattanooga School Bus Horror Was in Crash Just 2 Months Ago: Report
Walker was driving between 50 and 52 mph, about 20 mph over the posted speed limit, Warren told the court.
Onboard surveillance video showed Walker was on the phone that day, the officer said. It is illegal for school bus drivers to use their cell phones when children are onboard, he said.
The driver has been charged with vehicular homicide, reckless endangerment and reckless driving.
Hamilton County General Sessions Judge Lila Statom ruled Thursday there was enough evidence to send Walker’s case to a grand jury.
The grisly Nov. 21 crash also injured more than dozen children, authorities said. The dead ranged in age from 6 to 10.
Read: Funerals Begin for Victims of Chattanooga Elementary School Bus Crash
The bus was carrying 37 students from Woodmore Elementary school when it swerved off a street and toppled on its side before plowing into a tree.
The impact nearly tore the bus in half.
Walker’s attorney has said her client was “devastated by this tragedy.”
Jasmine Mateen, who lost her 6-year-old daughter in the crash and had two other kids onboard, told CBS News that Walker had asked the children a question as he was speeding.
“My daughter said right before the bus flipped that he was speeding around the curve and asked them, ‘Are y’all ready to die?” Mateen said.
Watch: Mom of Victim Deadly School Bus Crash: He Asked Them if They're Ready to Die
