WHITTIER, Calif. — The family of an autistic student who died after being left on a school bus for several hours on an extremely hot day has reached a $23.5 million settlement with the school bus company.

Hun Joon “Paul” Lee, 19, was found dead in an empty school bus on Sept. 11, 2015. His mother called his school when he did not come home that day. A driver checked the bus yard and found Lee, who was nonverbal, unresponsive in the bus. School bus drivers and police tried to revive him, but were unable to.

The bus driver, Armando Ramirez, was sentenced in January to two years in prison. As previously reported, he pleaded guilty to a felony count of dependent adult abuse resulting in death. He also admitted to an allegation of proximately causing Lee’s death.

Lee’s parents had filed a wrongful death lawsuit in December 2015 against the school bus company, Pupil Transportation Cooperative (PTC), and the Whittier Union High School District, according to the Los Angeles Times. However, the family’s attorney told the newspaper that the district was removed as a defendant when it became apparent that “the evidence was overwhelmingly against the bus company.”

The family’s attorneys released a police report of the incident that detailed a series of sexually explicit text messages Ramirez sent to another driver the morning he left Lee on the bus, Whittier Daily News reports.

The attorneys claimed that Ramirez was distracted by the messages, and that Pupil Transportation Cooperative (PTC), the school bus company, was lax in dealing with relationships between employees and their actions while on breaks. PTC previously disputed the attorneys’ allegation that it permitted employee relationships, but in a statement released on June 12, PTC said it changed its policies after the incident, but did not explain which policies had been changed, according to Whittier Daily News.

A statement obtained by the Los Angeles Times from Steve Bui, the chief executive officer of PTC, said that the company has worked to revise its policies so nothing like this incident happens again.

The school bus company admitted in a deposition conducted by the family’s attorneys that the incident with Lee was not the first time a student had been left on a bus, according to the Los Angeles Times. Debbie LaJoie, the director of transportation for PTC at the time of Lee’s death, said that to her knowledge, four special-needs students in addition to Lee had been left on a bus between 2006 and 2015, and none of the drivers involved had been fired after those incidents.

In September, Gov. Jerry Brown signed a bill into law (SB 1072, also known as the “Paul Lee School Bus Safety Law) that requires all school buses in the state to be equipped with child-check reminder alarm systems and for bus drivers to be trained on those systems. The new law goes into effect at the beginning of the 2018-19 school year.