Story highlights Driver was going "well above" speed limit, arrest warrant affidavit says

His mother says he called her shortly after the bus crash that killed five children

(CNN) Chattanooga school bus driver Johnthony Walker tried to pull the children off the bus, his mother told CNN. But there was too much blood.

Moments after the catastrophic crash Monday, Walker called his mother and told her what happened.

" 'Mama, I love you. I have been in a drastic accident,' " Gwenevere Cook recalled her son saying. "He texted me minutes later saying the kids are dead."

"He was trying to get (the children) off the bus -- all the bodies were limp," Cook said. "There was blood everywhere."