A California engineer accused of trying to kill a co-worker by slowly poisoning her over more than a year is in custody. Prosecutors say 34-year-old David Xu added toxic metal to the woman's food and water until she finally caught him on camera.

Prosecutors have not said what may have motivated the poisoning. Xu, a father of two, is an electrical, chemical, and mechanical engineer who has also served as an expert witness in numerous class action lawsuits. Now he's behind bars, with his bail set at $2 million, reports CBS News' Nikole Killion.

David Xu

Xu's attorney escorted his family out of a Bay-area courtroom earlier this week. On Thursday, Xu pleaded not guilty to charges of attempted murder and poisoning.

"As you all know, he's presumed innocent. These are allegations, only allegations," attorney Julia Jayne said.

Xu worked at Berkeley Engineering and Research where prosecutors say he spiked co-worker Rong Yuan's food and water on several occasions starting in October 2017. No one at the business would answer our questions.

"It's very unusual that we see a case involving the attempt to kill somebody by use of poison," said Teresa Drenick, Alameda County assistant district attorney.

Court documents say "for months" Yuan "noted a strange taste or smell from her water and food left unattended in her office" and "reported suffering immediate and significant health problems… at times requiring emergency care at a hospital."

She later "reviewed a surveillance camera in her office" and found "evidence of Xu adding a substance to her water bottle" on two occasions this year. Two of her relatives were also sickened after drinking from her water bottle. All had blood samples with "elevated levels of cadmium."

The toxic metal can cause kidney failure and other serious health problems, according to Dr. Michael Levine, who studies toxicology at the University of Southern California.

"It also has the potential to alter some of the DNA, and that's why it's potentially carcinogenic," Levine said.

"We want to make sure that this case sees justice so we will do all that we can within the confines of the criminal justice system to make sure that happens," Drenick said.

Prosecutors have not commented on the victim's condition. Xu's attorney said he has no criminal history and submitted several letters of support that she says speak to his character. His wife described him as a caring father and said his kids are "his pride and joy." Xu is due back in court early next month.