In a horrific crash that’s every parent’s worst nightmare, six children were killed and up to 20 others were injured after a school bus in Tennessee slammed into a tree at speeds well above the limit early last week.

The bus driver, 24-year-old Johnthony Walker, was arrested not long after on five counts of vehicular manslaughter along with charges of reckless driving and reckless endangerment, according to Chattanooga police Chief Fred Fletcher.

Nearly three dozen elementary school children, in grades ranging from kindergarten to fifth grade, were on the bus that overturned and crashed into a tree about a mile from Woodmore Elementary School in Chattanooga, Tenn.

“What has happened today is every public safety officials absolute worst nightmare, but that is nothing in comparison to the nightmare that families and friends in our community are facing,” Chief Fletcher said the day of the accident.

History of Complaints Against Driver Surfaces

Records released by the school district Friday revealed that students, parents, and administrators had expressed concerns over the behavior of the bus driver weeks before the fatal crash.

The first concerns related to Walker began in September after a parent wrote a letter to the school complaining that the driver had cursed at her kids and drove erratically.

“If another one of yall bus drivers curse my kids and slam on breaks making them hit they heads and fall out they’re seats I am going to beat his ass my damn self,” the parent wrote.

Other released records included two written statements from students complaining about Walker’s erratic driving.

“The bus driver drives fast,” one student wrote in November. “It feels like the bus is going to flip over. … He makes people go seat to seat back and forth, when someone is in the aisle he stops the bus and he makes people hit their heads.”

“The bus driver was doing sharp turns and he made me fly over to the next seat,” wrote another student. “We need seat belts.”

According to the Associated Press, a school official rode the bus after Walker complained students weren’t listening to him and reported the experience to the school district’s transportation supervisor on Nov. 2.

“The driver was now visibly upset and continued on by saying that he had another job and driving this bus was just a part-time job for him,” wrote Carlis Shackelford, a behavioral specialist at the school. “Driver stated that he could just leave him at the school. He then stated ‘or I can just leave the student on the bus and I will get off the bus and leave the school.'”

In a press conference, National Transportation Safety Board Chairman Christopher A. Hart said they were investigating whether fatigue played a role in the accident after Walker had taken a second job at an Amazon fulfillment center.

Some of these concerns, including Shackelford’s experience on the bus, were brought up to Hamilton County Transportation Supervisor Ben Coulter.

“We are addressing this issue with the driver,” Coulter wrote in an email. “Please keep me and Dominic D’Amico (of Durham School Services) informed on the progress.”

Investigation Into the Chattanooga Crash Continues

On Nov. 21, the National Transportation Safety Board announced it had launched a team to investigate the deadly crash. This will include a thorough look at Durham School Services, the bus company contracted by the Hamilton County School District, and its parent company National Express.

Authorities also removed the vehicle’s black box device, which will allow investigators to determine the vehicle’s speed, braking application, and other pertinent information. Issues with downloading the information have caused a delay in obtaining the data.

NTSB Chairman Christopher A. Hart says the final report on all the elements of the complicated crash could take up to a year.