A Californa bus driver was having sex with a co-worker as an autistic student was dying in a sweltering bus, according to a wrongful death lawsuit filed by the teen’s relatives.

Armando Abel Ramirez, 37, is currently serving two years in prison after he pleaded guilty in January to one felony count of dependent adult abuse resulting in the death of Hun Jun “Paul” Lee, a special needs student who was found dead at a Whittier bus yard in September 2015. Prosecutors said all of the windows in the bus were closed and temperatures that day hovered around 96 degrees.

A woman who worked with Ramirez is now testifying that she had sex with him as Lee – who could not verbally communicate – was left on the bus for nearly seven hours, CBS Los Angeles reports.

“She told the Whittier police that she felt bad because while she and Ramirez were laughing and having sex, Paul Lee was left on the bus and died,” court documents say.

Brian Panish, an attorney for Lee’s family in their lawsuit against the school district and bus company, said the woman has testified that she and Ramirez had left work previously to have sex.

“It’s terrible,” Panish told CBS Los Angeles. “It’s horrific that these people could sacrifice someone’s life to engage in this illicit activity.”

Panish said that text messages between Ramirez and the married colleague were obtained by the Whittier Police Department and prove the tryst happened. The messages were allegedly sent when the driver was at school to drop off Lee.

Ramirez, according to NBC Los Angeles, texted the woman at 8:42 a.m. that day to ask where she was.

“My bus,” she replied.

Two minutes later, she texted Ramirez, a substitute driver who was also working a split shift that day, “U sure your not working in the office today.”

“Clocking out,” Ramirez replied.

“He was very distracted and wanted to get with this woman as soon as possible,” Panish told NBC Los Angeles.

Nearly eight hours after Lee was left on the bus, Ramirez sent another message that read: “IT’S ALL ME [sic] FAULT.”

Lee and the woman had ultimately met up at Ramirez’s home, according to statements to police cited by KABC-TV.

“I was shocked and I just couldn’t believe that someone is in charge of taking care of people that need help would be so cavalier,” Panish told the station, adding that the “very explicit” text messages establish a timeline of the couple’s activities that day.

Panish claims that the bus company, Pupil Transportation Cooperative, is partially responsible for Lee’s death because it was aware of the “explicit, sexual relationship” between Ramirez and the woman — yet failed to stop it, compromising the safety of students.

Representatives of the bus company did not return requests for comment, NBC Los Angeles reports.

The civil trial is expected to begin next month.