WHITTIER, Calif. — A school bus driver who was arrested for the death of an autistic student on a school bus in September denied wrongdoing in charges against him in court on Monday.

Armando Abel Ramirez pleaded not guilty to the felony count of dependent abuse causing death, for the death of Hun Joon (Paul) Lee, 19, Sarah Ardalani, spokeswoman for the District Attorney’s Office, told the Whittier Daily News.

Lee, who was nonverbal, was left behind on a school bus for about seven hours on an extremely hot day. Police said that Ramirez was the driver when Lee rode the bus that day, according to the Los Angeles Times. As SBF previously reported, Ramirez, a former substitute driver for Pupil Transportation Cooperative (PTC), was arrested late last month, and Lee’s family has sued Whittier Union High School District and PTC.

Ramirez thought that Lee exited the bus, according to Whittier Daily News, but the prosecution alleges that Ramirez did not conduct a standard child-check procedure.

The tragic incident has prompted legislation that would require California school buses to be equipped with child-check reminder alarm systems. As SBF previously reported, the legislation was unanimously approved earlier this month by the Senate Transportation and Housing Committee. The bill is set for a hearing by the Senate Appropriations Committee on Tuesday. 

Ardalani told Whittier Daily News that, if convicted, Ramirez could face nine years in prison.

Ramirez is free on bail, and his preliminary hearing will be set at his next court date on May 27, the Los Angeles Times reports.