TENNESSEE — The driver charged with homicide in a Tennessee elementary school bus crash that killed five children and critically injured 12 others appeared to be speeding in the moments leading up to the wreck, police said.

Johnthony Walker, 24, was driving the bus full of students home from Chattanooga’s Woodmore Elementary School when, just before 4 p.m. CST, it veered off a road, flipped onto its side and smashed into a tree and telephone poll, according to a police affidavit.

Walker was driving on a narrow winding road at well above the speed limit of 30 miles per hour (48 km per hour) when he lost control, leaving the bright yellow bus mangled and nearly severed in two, the affidavit said.

Walker, who was cooperating with authorities, was charged with five counts of vehicular homicide, reckless endangerment and reckless driving.

As the city mourns, chilling reports have emerged alleging that Walker asked the students, “Are y’all ready to die?” before swerving off the road into a tree.

Jasmine Mateen, the mother of three children aboard the bus, lost her 6-year-old daughter in the crash. She told CBS News what one of her other children had to say about the driver.

“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 to CBS correspondent Mark Strassmann.

School officials have found no record of complaints against Walker, said Melydia Clewell, spokeswoman for the Hamilton County District Attorney’s office. It was not immediately clear how long Walker, who was working for a private company hired by the school district, had been licensed to drive school buses.

The bus was not equipped with seatbelts but did have two cameras on board as well as an engine chip that could contain information, Christopher Hart, chairman of the National Transportation Safety Board, said during a news conference on Tuesday.

He urged witnesses or anyone with information about the crash to contact police.

The school district, which remained open on Tuesday, set up a fund for the victims and planned an evening vigil.

“We are heartbroken for all of our students and their families,” Hamilton County Schools Interim Superintendent Kirk Kelly said at a news conference on Tuesday at the elementary school. “Yesterday was the worst day that we had.”

Kelly said five children were killed: A kindergartner, a first-grader and three fourth-grade students.

Six students were in critical condition and another six were hospitalized with less severe injuries, Kelly said.

Walker’s mother, Gwenevere Cook, told CNN that her son had tried to rescue students from the bus after the crash but blood and the children’s limp bodies made it difficult.

Cook described her son as a responsible father of a 3-year-old who held down two jobs and had never been in trouble.

While Cook said she grieved for the victims and their families, she also sought mercy for her son, who is being held on $107,500 bond.

“I am asking for compassion also for my son,” she said.

Residents in and around Chattanooga, a city of about 170,000, sent their condolences and provided aid to the school children and their families.

People lined up at blood donation centers that stayed open late on Monday night, local media reported, and one woman donated 45 teddy bears to the school to comfort students.

“There are no words to comfort the broken heart of a mother or father,” Chattanooga Mayor Andy Berke said at a news conference. “So today our city is praying for these families.”