Chattanooga, Tennessee (CNN) A Chattanooga school bus had not been traveling on its designated route when it crashed, killing six children and injuring dozens, investigators said.

The bus was on its way to drop off children after school Monday when driver Johnthony Walker swerved off the road and the vehicle plowed into a tree.

The bus, carrying 37 students, was not supposed to be on the narrow Talley Road, according to crash investigators.

"We are investigating why it was not on the designated route," National Transportation Safety Board Chairman Christopher A. Hart said.

Sixth victim identified

Five children died Monday. A sixth child died Wednesday from injuries sustained in the crash, police tweeted.

That victim, Keyonte Wilson, "was a tough little boy," family member Kevin McClendon told CNN. "I know he's in a better place."

The other children who died have been identified as Zyaira Mateen, 6, D'Myunn Brown , 6, Keyonte Wilson, 8, Zoie Nash, 9, Cor'Dayja Jones, 9, and Zyanna Harris, 10, according to their families.

While most of the injured have been released, five remain hospitalized -- some with severe head or spinal injuries

"We certainly understand on this week of Thanksgiving (that) we all need to be with our families, appreciating them, thinking about our kids, because there are a lot of families hurting in our city right now," Mayor Andy Berke told CNN on Wednesday.

No alcohol or drugs in driver's blood

Police Sgt. Austin Garrett said no traces of alcohol or drugs were found in Walker's blood.

But investigators allege that Walker was driving "well above" the speed limit.

"Mr. Walker lost control of the bus and swerved off of the roadway to the right, striking an elevated driveway and mailbox, swerved to the left and began to overturn, striking a telephone pole and a tree," according to an arrest affidavit for Walker.

Walker faces five counts of vehicular homicide, as well charges of reckless endangerment and reckless driving. A sixth vehicular homicide charge likely will be added, police spokeswoman Elisa Myzal said.

Walker's mother, Gwenevere Cook said her son tried to get the children off the bus after the crash. She said Walker is a respected man and the father of a 3-year-old son. He worked two jobs and had never been in trouble before.

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Garrett said investigators have not yet interviewed the children on the bus.

Investigators are also reviewing data devices on the bus, including video of front, back and side views of the vehicle. The NSTB was having a problem downloading video and data from the cameras and the engine control module on the bus because of damage, Hart said.

There had been no other fatal crashes on the same road over the past three years, according to the NTSB.

Walker's driving history scrutinized

Bus driver Johnthony Walker has been charged with vehicular homicide.

Walker received his commercial driver's license in April, the NTSB said.

His school bus left Woodmore Elementary School on Monday afternoon and did not make any stops before the crash, Hart said. The accident was the second time in two months that Walker crashed a school bus.

In September, Walker was driving around a blind curve in a residential area when he failed to yield the right of way and sideswiped another car, according to the accident report

In the earlier crash, which Garrett described as a "minor wreck," Walker "crossed over into the oncoming traffic lane to maneuver the bus through the curve and struck vehicle #2 in doing so," the report states. "There were no children in the front rows, and no reports of any injuries. The damage (was) minor to both vehicles."

First lawsuit filed

The first lawsuit stemming from the crash was filed Wednesday by the family of Jamar Boling, 8, who was injured in the accident. The complaint, which alleges that Boling sustained significant physical and psychological injuries, names the driver and Durham School Services, which operates the bus service.

The bus company received a "conditional safety rating" in 2007 from the Federal Motor Carrier Safety Administration. It was later upgraded to "satisfactory" after unspecified problems were resolved, Hart said. A website lists the most recent satisfactory rating date as July 31, 2015.

"We will be exploring what were the deficiencies," he said.

Durham School Services CEO David Duke said in a YouTube statement that the company, which runs the bus service, was cooperating with federal and local investigations.

"My responsibility now is to look for answers -- answers about why this tragedy occurred and answers for how we can make sure that this never, ever happens again," he said.

Duke said he could not comment further.

"I don't want to compromise that investigation," he said. "What I can do is promise that I'm determined, that we're determined to find out what happened. And that we will offer any support that we can to the families."