The driver was rushed to the hospital, where he was pronounced dead.
Omnitrans identified the driver as 48-year-old Lawrence Kester of Fontana. Kester had worked for the company for 15 years and had earned more than a dozen commendations for safety and customer service.
"We are devastated by this horrible and senseless attack. We will remember Larry as a man who was deeply dedicated to his family, friends and customers," said Omnitrans CEO/General Manager Milo Victoria. "Our prayers and deepest sympathies go out to his family and loved ones."
The suspect got off the bus and ran through a nearby Bank of America branch and into a Stater Brothers supermarket. Employees in the store subdued him until police arrived and arrested the suspect.
"He was just being an innocent person and this guy wants to hurt him like this. It's wrong," said Mariama Wells, who knew Kester. "He is somebody that I saw a lot. He helps everybody. He is nice. If you're short 25 cents he would let you slide. He wouldn't have done anything for that man to do that to him."
Investigators said they are not sure what sparked the attack.
"He is acting very bizarre. He's making a lot of spontaneous statements. What led up to this, if he is under medication or if he's under some psychological medicine or having some mental issues, I don't know," said Lt. Joe Cirillo of the Rialto Police Department.
Officers are still investigating and have not released the name of the suspect.