Walker faces more than 30 charges including six counts of vehicular homicide.
Prosecutors say he was speeding and on his phone.
As the trial begins, WREG has uncovered a scathing federal investigation about Walker's employer Durham.
The same company that transports children all across Shelby County.
Through the Freedom of Information Act, NewsChannel 3 obtained reports compiled on Durham by the Federal Motor Carrier Safety Administration.
The FMCSA cited Durham in eight violation categories after the crash and identified numerous breakdowns of policies and procedures.
In a post-crash investigation, the FMCSA found Durham didn't have a consistent means of documenting and tracking complaints.
For example, a supervisor admitted to getting speeding complaints on Walker, but writing them in a spiral notebook, instead of putting them in his file.
Durham employees got a complaint about Walker five days before the fatal crash and pulled the video, but never watched all of it.
Investigators noted the final six minutes revealed children "shouting ... falling out of their seats and into the aisles ... appearing to indicate the bus was swerving."
The manager who'd initially only watched the first 20 minutes of the video (prior to the fatal) later admitted to FMCSA investigators "he probably would have terminated Walker prior to the fatal crash if he had been aware of its contents."
To thoroughly track and investigate complaints, regulators recommended Durham create a single source complaint and discipline management system.
It also suggested Durham create a "stand down" policy to temporarily remove drivers after getting verifiable complaints about reckless or dangerous driving.
The NewsChannel 3 Investigators shared the findings with Senator Lee Harris who introduced a bill after the crash to set the minimum driver age to 25. A similar House version of the bill passed and the law went into effect Jan. 1.
Harris called the reports eye opening.
"If somebody had watched that video and had seen the kids getting thrown out of their seats because you know there was swerving going on, that, maybe this could have been avoided. That the driver could have been suspended, retrained and disciplined."
Speaking of training documents reveal Durham was conducting what it called "mandatory" monthly safety training, but Walker never attended.
Managers were often forced to overlook their regular duties and serve as drivers, due to the terminal being short staffed. They admitted to keeping "sub-par" drivers on the payroll.
The investigation also noted Durham employees are typically only paid for six hours of work, so most have other jobs.
Yet, Durham didn't have a policy inquiring about outside employment.
According to the report, Walker worked night shifts for at least one employer.
Senator Harris asked of the issue, "The question is, how fatigued are they when they get behind the wheel?"
Investigators also uncovered several violations with Durham's protocols for drug and alcohol testing both prior to employment and after a crash.
After a subsequent comprehensive review, the FMCSA lowered Durham's safety rating and fined the carrier just over $6580 for using a driver who tested positive for a controlled substance.
"Hopefully a lot of these things have been corrected, but of course this is a recent report and the violations they found were pretty flagrant," said Harris.
Durham told WREG its corrected all the violations. The carrier regained a "satisfactory" safety rating in October 2017.
A spokesperson says Durham's also addressed a number of federal recommendations like mandatory monthly safety meetings and asking employees about outside work, as well as others.
The biggest change though, according to the spokesperson, is the fact that the company launched busreport.com, where anyone can submit complaints for Durham to log, track and investigate.
Harris says he plans to read the reports again, and suggests school districts do the same.
"I think it calls for a serious, a serious review by the school boards charged with responsibility of renewing contracts like this."
The Hamilton County School Board renewed its contract with Durham last spring. Shelby County's contract runs through July of this year, with an option to renew through 2022.