A deputy district attorney on Friday said there is “no question” that two Covina-Valley teachers had sex with students during a December campout, but that her office did not file more serious charges because investigators could not prove the women knew one of the boys was underage.

The Orange County District Attorney’s Office on Wednesday charged Melody Lippert, 38, and Michelle Ghirelli, 30, with contributing to the delinquency of a minor, a misdemeanor with a maximum penalty of one year in jail. Gone were the arresting agency’s charges of oral copulation and unlawful sex with a minor against Ghirelli and conspiracy against Lippert. Both sets of crimes hinge on the women knowing the age of the victim, said deputy district attorney Kristin Bracic.

“You have to prove not only that they engaged in sex, but that at the time she knew he was under the age of 18,” she said.

Ghirelli works in Covina-Valley’s district office, while Lippert is a teacher at South Hills High School.

The two women were set to appear in court for the first time Friday, but their arraignment was changed to Feb. 17 due to a scheduling mistake.

Ghirelli allegedly told investigators she “just assumed” the boy she had sex with was 18, according to Bracic.

“She offered up various reasons,” Bracic said. “He was months away from turning 18, so without a little more information, it’s just under the line of where we’re comfortable filing.”

Ghirelli’s attorney, Stephan DeSalle, declined to comment when reached by phone Friday. A call to Lippert’s attorney was not returned.

The district attorney’s office also did not charge Lippert with conspiracy — a charge that likely would have become aiding and abetting— for her part in facilitating the camping trip because it could not prove the South Hills High School teacher knew the age of the 17-year-old student.

Stan Goldman, a Loyola Law School professor of criminal law and former L.A. County public defender, said California’s statutory rape laws changed following the 1964 case “People v. Hernandez.” Since then, a defendant could use mistaken age as a reasonable defense against such charges, as long as the victim was older than 14.

“It’s not that she’s not guilty, it’s just that she has an arguable defense, and a prosecutor might simply say — well, he’s 17-and-a-half and looks 20, and it’ll be tough for us to overcome the argument that she didn’t realize his age,” Goldman said. “It may not be a great defense, but on the other hand, I will say that I don’t think there’s a whole lot of eagerness to lock up women for having sex with a 17-year-old guy. It just doesn’t seem to be the public concern. Now if it was a girl (female student) with a guy, I think jurors are more likely to convict.”

Those factors work against a district attorney without enough evidence to overcome the mistake-of-age defense, Goldman said.

The more serious charges may still resurface by the date of Lippert and Ghirelli’s arraignment, according to Bracic. The investigation is ongoing and the district attorneys’ office continues to receive new evidence, she said.

Lippert allegedly organized the two-day San Clemente Beach trip in December through a group text message with the five teens and Ghirelli.

“I would say between the two that Ms. Lippert is sort of the brains of the operation,” Bracic said.

The Orange County Sheriff’s Department alleged that Lippert first had sex with one of the boys — an 18-year-old — at a camping trip in November before organizing a second trip with Ghirelli. Deputies arrested the pair on Jan. 17.

Bracic said there is some indication that another Covina-Valley teacher dropped off or picked up Ghirelli and Lippert from the beach, but she could not confirm if it was one of the teachers currently on administrative leave.

“Whether they knew there were students there, whether they knew what was going on, I’m not aware of at this time,” she said.

Bracic will meet with Covina-Valley’s administrators Tuesday to learn what the district’s separate investigation has uncovered.

Covina Unified Education Association contract specialist Michelle Ramos called that investigation into question Thursday, as the union alleges the district has yet to speak to any of the teachers currently facing discipline. Ramos’s response came after district officials said they would start the process of firing five teachers, including Lippert and Ghirelli, at their Feb. 17 meeting.

The other teachers facing termination include art teacher Sean Kane, who allegedly posted on Facebook that the boys on the camping trip should have kept their “stupid mouths shut and enjoyed it”; and Larry and Lisa Anderson, a married couple who teach at South Hills and Ben Lomond, respectively. The district has not disclosed the reason the couple was put on paid leave.