Two people from Washington state were arrested on suspicion of sex crimes involving children after a man was allegedly texting about molesting children during a Southwest Airlines flight from Seattle to San Jose, California.

A female passenger told police she had caught 56-year-old Tacoma resident Michael Kellar, who was sitting in front of her, texting about sexually assaulting children with large font on a smartphone, The Associated Press reported.

San Jose sex-crimes Detective Nick Jourdenais said the passenger reported the text messages moved from sexual fetishes to much worse.

"It was in large font, and she sees certain words and starts contemplating there's something bigger there," he said. "Then the conversation transitions to children. That's the moment when she decided to preserve the evidence as best she could."

The passenger took photos of some of the texts with her phone and then alerted flight crew, who then notified an officer stationed at San Jose airport. Police at the airport arrested Kellar on suspicion of attempted child molestation and solicitation of a sex crime, both felonies.

During the investigation, which involved FBI agents in San Francisco and Seattle, Kellar freely consented to a phone search and reportedly dismissed the text messages as merely fantasy and role playing.

Gail Burnworth, a 50-year-old of Tacoma, was then identified as another suspect, ABC 7 reported.

Burnworth was arrested in Pierce County, Washington on suspicion of sexual exploitation of a minor, rape of a child and dealing in depictions of a minor engaged in sexually explicit conduct, San Jose police said.

Two children, ages five and seven, who lived at Burnworth's home were identified as victims. Investigators believe Kellar was making sexual requests of the children and Burnworth carried them out.

Police are praising the passenger, a Seattle-area preschool teacher who asked not to be identified, as a hero, The Mercury News reported.

"It's kind of mind blowing," Journdenais said. "She gets on a plane, a normal citizen minding her business. A couple of hours later, she's intervening on quite possibly the most traumatic thing children can go through. This was life-altering for them."