By Brian Maass & By Mark Ackerman

DENVER (CBS4) – A budget analyst with the Colorado Department of Education has been criminally charged with 42 criminal counts, including sexual assault and invading the privacy of female colleagues for sexual gratification, by repeatedly taking pictures up their skirts with his iPhone.

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Thanh Ta is being held in the Denver jail on $500,000 bond. Prosecutors say he not only victimized numerous women while working at his government job, but hundreds of other unsuspecting women in public places like coffee shops, grocery stores and on the 16th street mall.

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“This creep had a file with my name and hundreds of photos,” said Amy Skinner, who worked at the CDE for two and a half years and considered Ta a close friend. Police and prosecutors now say Skinner is one of Ta’s many victims.

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“I had absolutely no idea whatsoever that he took hundreds of photos of me over a couple year time period… up my skirt, going up a staircase, going up my skirt, down my shirt, between my legs in an office,” said Skinner. “I can’t believe how good he is at using an iPhone and taking photos without women’s knowledge. It absolutely blows my mind.”

Amy Skinner (credit: CBS)

CBS4 does not normally identify alleged victims of sex crimes, but Skinner asked that she be named as a means of standing up for herself and other unnamed victims.

“That’s the part that just keeps percolating in my mind non-stop. I should have been safe at work. I wasn’t at a bar. I should have been safe at work. I should have been safe in a stairwell at work,” she said.

CBS4’s Brian Maass interviews Tracy Ta. (credit: CBS)

Equally stunned is Ta’s wife, Tracey, who spoke to CBS4 saying she had no clue about her husband’s double life.

“There was never a time that I ever suspected anything. I never saw him doing anything inappropriate,” Tracey said. “I never saw him taking any kind of pictures that I would have questioned.”

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She recounted how her husband’s secret life first emerged. She said in September, he came home from work and told her he had been placed on administrative leave for inadvertently downloading a computer virus onto his work computer.

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She accepted the explanation, but several nights later, Ta said police knocked on her door late and told her they had a search warrant. Police seized hard drives and investigators explained what had occurred.

She said she felt “shock, disbelief, betrayal, anger. Each time I hear a name, each time I hear what he has done, it’s just so heartbreaking. They were violated in places that they had every right to feel secure and comfortable.”

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Ta said her husband, a Vietnamese immigrant, was widely loved, devoted and caring. The pair met at the Department of Education nine years ago and had been together ever since.

“I just feel such heartbreak for these people involved and can’t really wrap my head around why he would do it,” she said.

She has initiated divorce proceedings.

Denver prosecutor Carlos Rueda labeled Ta as a “predator” and says Ta had photos of roughly 60 women catalogued by name on his hard drive and that there may be more; the FBI was still trying to access a second hard drive which could contain additional photos.

Denver police investigators interviewed Ta last October and according to their notes, Ta admitted taking pictures of his female co-workers under their skirts when he walked up and down stairs “without them knowing.”

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Officials records state, “Thanh said he has a problem and knows this is not normal.”

He told police he began taking the ‘upskirt’ photos in 2011 on his iPhone. According to police, Ta said he did not share the pictures with anyone and did not put them on the internet. Ta declined an interview request from CBS4.

Jeremy Meyer, a spokesperson for the CDE, told CBS4 that the department learned what their employee was doing when Ta connected his external hard drive to the CDE computer system.

Meyer said the department immediately placed Ta on administrative leave and contacted police. Ta was later allowed to resign.

He has pleaded not guilty to all charges and is due in court Jan. 26 for a motions hearing.

CBS4 Investigator Brian Maass has been with the station more than 30 years uncovering waste, fraud and corruption. Follow him on Twitter @Briancbs4.

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Mark Ackerman is a Special Projects Producer at CBS4. Follow him on Twitter @ackermanmark