UPDATE: It could be more than a year before the NTSB releases the cause of the crash that killed six children and hurt more than 20 others.

NTSB investigators returned to Washington, D.C. last week with their evidence and measurements.

Former chairman, Jim Hall said the agency is now looking at the facts of the case.

Hall does not currently serve on the board or have a role in the investigation.

"There's an important issue here, in my opinion, in regard to oversight. Did Hamilton County attempt to essentially delegate their responsibilities in regard to safety to this firm in Chicago?," Hall said.

Bus contractor, Durham has not agreed to Channel 3's request for an on-camera interview. Instead, they have answered questions through email and sent video statements.

In one of those statements, Durham promises safety changes nationwide including smart cameras. They will be installed in Chattanooga by the end of the month, according to Durham representatives.

"These cameras record both the driver and the road each time they sense unusual driving giving us a record of what happened, so it can be promptly addressed," David Duke, Durham School Services President and CEO said.

As for the investigation, Hall said it'll look at speed, the driver, and the contract.

After that, the five members of the NTSB board will review it and give recommendations in a public meeting.

"All of these events are going to be closely looked at by the NTSB and I hope that the final analysis of the board will come to the same conclusion I came to in 1999 that it does not make sense to say we put our children first and not protect them on our yellow school buses," Hall said.

The biggest roadblock for putting seat belts on school buses is money. Right now, only 6 states require them. 

Records show the driver, 24-year-old Johnthony Walker, had several complaints filed against him before the crash in November.

The NTSB said Talley Road was not on Walker's route, but a spokeswoman for Durham said it was a part of his normal routine.

While Hamilton County school officials said they forwarded all complaints to the company, Durham representatives said they only received six. Two of those complaints talked about Walker speeding.

Another change Durham plans to implement is a cloud-based complaint system that teachers and administrators can directly report any issues with buses or drivers. It went online Monday and will go nationwide by the end of 2017.

They also plan to hire 30 extra bus monitors in addition to the 70 they already have in the district.

PREVIOUS STORY: The NTSB announced Thursday it has completed the on-scene phase of the agency’s investigation of the fatal, Nov. 21, 2016, school bus crash on Talley Road, Chattanooga, Tennessee.

Six students died and more than 20 others were injured as a result of the single-vehicle accident in which a Hamilton County School bus, operated by Durham School Services and driven by a 24-year-old driver, hit a mailbox, a utility pole, rolled onto its right side and then collided with a tree.  The bus was carrying 37 students at the time of the crash.

NTSB investigators departed Chattanooga early Monday after completing the following work items: 

Vehicle Factors Group

  • Finished school bus examination, including documenting tire DOT numbers.
  • Confirmed the brake-throttle valve recall and, confirmed a replacement valve was installed as required.

Recorders Group

  • The engine control module was successfully downloaded and the data are being evaluated.
  • The NTSB’s Recorder Laboratory in Washington received the school bus video recorders and has begun downloading data.
  • Confirmed the identity of the bus anti-lock brake module manufacturer and determined the module does not contain useful electronic brake data.

Highway Group

  • Worked with the school district to receive the last 30 days of GPS download for the school bus and the route driven by the school bus driver prior to the Nov. 21 crash.
  • Continuing to examine materials received from the City of Chattanooga Transportation Department.
  • Survival Factors Grou
  • Continued working on seating chart for the 37 student passengers.
  • Human Performance Group
  • The NTSB requested an interview with the school bus driver, however, the driver declined to be interviewed on advice of legal counsel.  The NTSB continues to pursue an interview with the school bus driver.
  • Subpoenas were delivered to local hospital and mental health facility to obtain medical history of the driver.  Local pharmacies were canvassed for driver records, subpoenas delivered as appropriate.  A subpoena was delivered for the driver’s AT&T cellphone records.  A subpoena was also delivered to Amazon to obtain the bus driver’s employment record.
  • Interviewed the school principal regarding driver behavior towards students and general driver concerns.

Witness Group

  • Three witnesses to the crash response, but who did not witness the crash itself, were interviewed.  Investigators are working with the Department of Child Services to set up interviews with student passengers.  Investigators are also working with Chattanooga PD, facilitating follow-up interviews regarding the crash events and evacuation, with students who were on the bus.

Other Activities

  • Chattanooga PD and Leica scanned an exemplar school bus and accident school bus in upright position.  Received all scan data from Chattanooga PD.
  • Final work progress meeting held.

A preliminary report is expected to be published within the next few weeks, no further updates are planned until then.  Following the publication of the preliminary report, the next update will come with the opening of the accident docket and notice of the NTSB Board meeting.  The final report is likely to be ready for board review within 12 to 18 months.