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Orange County Superior Court Judge Gregg Prickett listens to a victim impact statement during the sentencing hearing for former UCI professor Rainer Klaus Reinscheid Tuesday, Aug. 20, 2013 at Orange County Superior Court in Santa Ana, Calif. Reinscheid, who set fires at his late son's school, a school administrator's home and a nearby park, said he was so overwhelmed with grief after his 14-year-old son killed himself that he wrote and did things he would not normally do. (AP Photo/The Orange County Register, Sam Gangwer) MAGS OUT; LOS ANGELES TIMES OUT

SANTA ANA -- A UC Irvine professor facing up to 18 years in prison for setting a series of fires after his son killed himself is pleading for leniency, saying he was overwhelmed with grief and did things he would not normally do.

Rainer Reinscheid apologized for his actions Tuesday during a nearly three-hour sentencing hearing that included speeches from his friends and colleagues, as well as school officials who said the fires -- and threats written in Reinscheid's emails -- terrorized them.

The hearing is set to resume Wednesday afternoon.

Reinscheid, a pharmaceutical sciences professor at the University of California, Irvine, whose private emails described graphic plans to attack his late son's high school and kill students, told the court that the irrational thoughts that drove his behavior in the weeks after his 14-year-old son committed suicide have disappeared.

Now, Reinscheid said he wants to return to his native Germany and find work to support his family and care for his younger child, acknowledging his academic career is over.

Reinscheid, 49, is on unpaid leave from UC Irvine.

"I lost my son, and then I lost myself," Reinscheid told the court. "Now, I am asking you, your honor, and many other people, to forgive me and show mercy."

Reinscheid faces a prison sentence that could range from three to 18 years after he pleaded guilty last month to six counts of arson, three counts of attempted arson, and resisting or obstructing an officer.

Colleagues and friends described Reinscheid as a brilliant scientist, a dedicated researcher, a trustworthy friend and devoted and doting father who was distraught after his son's death. The teen hanged himself with a belt in an Irvine park in March 2012 after he was disciplined by an administrator at University High School for allegedly stealing from the school store.

School officials and teachers, however, said the series of fires Reinscheid set -- and the emails that described Reinscheid's plan to buy machine guns, shoot students, commit sexual assaults and burn the school before killing himself -- drove people in the 2,800-member campus to live in fear.

"That tragedy (his son's death) cannot serve as justification for terrorizing a school community and staff members who have dedicated their lives to helping others," Irvine Unified Superintendent Terry L. Walker wrote in a statement read aloud to the court by a fellow administrator.

No charges were filed directly related to the emails. Reinscheid's wife, Wendy, told the court she and her husband were encouraged to write down their thoughts by a therapist to help them get out negative feelings after the boy died.

But prosecutor Andrew Katz told the court these writings can't be brushed off as mere musings. He noted they came after two high school students kept a journal chronicling their plans to attack Columbine High School, and after a shooter told a therapist about his violent thoughts and later sprayed gunfire on patrons at a movie theater in Aurora, Colo.

Reinscheid has worked at UC Irvine for about a dozen years. His research included studying molecular pharmacology and psychiatric disorders, including studies of schizophrenia, stress, emotional behavior and sleep.