At times tearing up, the former San Jose elementary school principal on trial for failing to report suspected child sexual abuse tried to explain Thursday what in hindsight seems unimaginable -- why she didn't call police to report that a teacher had blindfolded an 8-year-old student with no one else there, made her lie down on the classroom floor, touched her feet with something that felt like a tongue, inserted something gooey in her mouth and then wiggled her head around til she tasted a salty liquid.

"It was my job to keep those kids safe," Lyn Vijayendran testified in a choked voice. "But on that day, I did what I thought was right.

"Now, looking back, I have a different lens."

For more than two hours Thursday, the former 36-year-old principal of O.B. Whaley Elementary struggled to convey why she accepted teacher Craig Chandler's explanation for his disturbing behavior -- that it was part of a lesson plan about Helen Keller.

"He was very forthright," she said, once again tearing up. "He looked me right in the eye."

For only the second time in two decades, Santa Clara County prosecutors have charged a local educator with shirking their legal obligation to call the authorities when they have a reasonable suspicion that a child has been abused.

Prosecutors have taken the rare step of making an example out of Vijayendran primarily because her alleged lack of judgment in October 2011 had devastating consequences. Another child reported being molested in a similar fashion by the same teacher about three months later.

Chandler was subsequently arrested in January and ultimately charged with committing lewd and lascivious acts on five children. Tests by the Santa Clara County crime lab found his semen on a classroom chair. The 35-year-old teacher, in jail pending his trial, faces a maximum sentence of 75 years to life if he is convicted.

If Vijayendran is convicted of her misdemeanor charge, she could serve up to six months in jail, though it is more likely she'd be put on probation. She has been reassigned to the district office as coordinator of teacher support programs.

On Thursday, under gentle questioning by her attorney Eric Geffon, the former principal said she was lulled by several factors into believing the teacher had merely done something dumb.

One reason Vijayendran was convinced was the child's demeanor was completely out of character for someone who had been molested.

"She had a big smile on her face," she told the jury of five women and seven men. "She was her normal self, very talkative, the same as if she was talking about what she'd perform at the talent show."

The girl and her mother, who were both interviewed by the principal, didn't contend the incident had been sexual in nature, she said, merely that it had been strange. The mother is a legal immigrant.

Vijayendran also hadn't gotten any training from Evergreen Elementary School District on how to interview suspected victims and other aspects of her responsibilities as a mandated reporter.

She also said she interviewed the teacher because she was told to do so by the district's human resources director, Carole Schmitt. In hindsight, that decision gave Chandler the opportunity to try to get rid of any incriminating evidence.

Her interview with Chandler was very persuasive, Vijayendran said. He told her that he called the girl into the classroom to prepare a lesson on Helen Keller, which he had been using for years. He said the "instructional goal" was to deprive participating students of sight. He said he used a bath sponge on her foot and legs, and put a bottle containing salty water into her mouth. All the while, his classroom door was open, he told Vijayendran, though the child said the door was closed.

"He said students learned better by doing," she said. "He was very convincing."

But under cross-examination by prosecutor Alison Filo, the former principal admitted she was worried before she spoke to Chandler about the sexually suggestive aspects of his behavior toward the girl.

Among other concerns, the child reported the teacher told her to "open her two legs."

"If someone said that to you in a grocery store line, you'd slap him, wouldn't you?" Filo commented.

"You'd have to be crazy not to think that (his behavior could be sexual)," Vijayendran agreed.

That admission contradicts Geffon's insistence that it never occurred to anyone -- the principal, mother or human resources director -- that the strange encounter was sexual.

Vijayendran also apparently didn't ask Chandler what wiggling the child's head while something was in her mouth had to do with Helen Keller. And she didn't query other administrators if it was true they knew all about the lesson plan and were fine with it, as Chandler claimed.

Schmitt, the district's director of human resources, also didn't help Vijayendran's case much, though the jury may wind up sympathizing with the former principal. The administrator testified she told Vijayendran to interview Chandler, but all she knew at the time were a few scant details. Vijayendran merely told her that Chandler put something "salty, warm and hard" in the child's mouth. Schmitt said she hadn't received any training on reporting child sexual abuse for 17 years.

But Schmitt said it was Vijayendran, not her, who decided how to handle the incident. After the interviews, Vijayendran called Schmitt and without sharing many details said she'd decided to grant the mother's request and transfer the child to a different classroom. She also reported ordering Chandler never to use the lesson plan again.

"The only direction I gave her," Schmitt said, "was talk to the teacher and talk to the child."

The case could go to the jury as soon as Friday afternoon after the judge instructs the jury and the lawyers make their closing arguments.

Follow Tracey Kaplan at 408-278-3482. Follow her at Twitter.com/tkaplanreport.