Federal prosecutors are expected to file charges against a Pierce County man and woman who police say were plotting to sexually abuse children.

50-year-old Gail Burnworth was re-arrested Friday just before 6 p.m. for a federal warrant for conspiracy to produce child pornography, according to the FBI. She's scheduled to appear in federal court on Monday when prosecutors will release more information.

A spokesperson for the Pierce County Prosecutor's Office said she was originally released Thursday night because they reached the 72 hour limit on how long they could hold her pending further investigation.

Related: 2 arrested after sending disturbing texts on flight from Seattle

The detective leading Washington state's task force on Internet Crimes Against Children said the case is still solid and the couple could face federal charges as early as Friday.

"My experience has been individuals who engage in this type of criminal activity they're obsessed people," said Seattle Police Captain Mike Edwards.

Edwards tried to explain the mindset of someone who sexually abuses a child–why 56-year-old Michael Kellar, who was on a Southwest flight–would have allegedly pulled out his cell phone and started texting someone about his disturbing plans.

Fortunately, an observant female passenger sat behind him.

"It was a very large phone with very large font," said Edwards. "So it was hard on an airplane not to see it anyways. But for her, now she was kind of dialed in. She noticed the comment in the messages that appeared to be something that was going to be putting the children in danger. That there was going to be harm done to these children. So at that point, she pulled her phone out and started taking pictures of the messages herself."

That good Samaritan notified the flight crew and police were waiting to take Kellar into custody when they landed in San Jose.

Burnworth, who Kellar allegedly sent the texts to in Tacoma, was also arrested.

Edwards said Kellar picked the wrong seat on that flight, because the observant passenger behind him was a Seattle pre-school teacher.

"That citizen happened to be a pre-school teacher," said Edwards. "For her, her kids are her life. And because the messages involve children, that got her attention even more."

Police praised the pre-school teacher.

"Because she did what she did, she saved these children from horrific abuse," Edwards said. "For that, she should be commended."

Edwards said Kellar and Burnworth met on a dating site about a year ago.

It was Burnworth who knows the alleged victims.

Kellar has a court appearance in San Jose Monday, according to the Santa Clara District Attorney's office.