JACKSONVILLE – A 13-year-old Jacksonville High School student is in custody and facing a possible terrorist threat charge after posting a still photo from video of the 1999 Columbine shooting to Snapchat, Jacksonville police said Monday.

The post created a stir among Jacksonville High parents over the weekend, after a second person, apparently alarmed at the photo, reposted it with a warning to students not to come to school Monday.

“That’s all you need, just to post something like that, for it to be a terrorist threat,” said Jacksonville police Chief Tommy Thompson.

According to a report by Jacksonville police, a Jacksonville High parent came to the city’s public safety complex last week to report a social media post his sons had seen. The post appeared to be a still shot from the Columbine attack.

“The image appeared to have no text with it,” the police statement read. “A separate female had in turn shared this photo with the following text: ‘This is a student at JHS be very aware of your surrounding all throughout Monday and next week SPREAD THE WORD.”

Students and parents apparently did spread the word. By Sunday evening, parents on Facebook groups were discussing an alleged threat at the school, with some saying they’d keep their kids home on Monday as a result of the threat. It’s unclear how many parents actually did that; attempts to reach Jacksonville City Schools superintendent Mark Petersen for comment Monday morning were unsuccessful.

Thompson said the person who reposted the photo, with the Monday warning, wasn’t charged. He said police were confident she shared the photo because she was alarmed by the picture.

The 13-year-old’s mother brought her son to the public safety complex late Saturday night, Thompson said, where the boy was taken into custody and transferred to Coosa Valley Youth Services, a juvenile detention center.

Assistant police Chief Bill Wineman said the 13-year-old acknowledged posting the original image.

“His comment was ‘I was just kidding,’” Wineman said.

Thompson said police are seeking a terrorist threat charge against the boy. Assistant District Attorney Randy Moeller said he couldn’t comment on the matter because it’s a juvenile case.

“I can say that if you make a threat against a school, involving any kind of violence, our position is that we are going to lock you up,” Moeller said.

Moeller said Coosa Valley is filled to capacity, in part because of a surge of alleged school threats over the past few weeks — in particular, since the school shooting in Parkland, Fla., last month.

Wineman said he believed it’s important to seek felony charges against people who allegedly make school threats, because a conviction would keep them from ever legally possessing a gun. Wineman said seeking mental health adjudications instead is unworkable, because the mental health system is so underfunded.

“A felony conviction means he can’t vote and can’t do a lot of other things either,” Wineman said.

It’s unclear whether that would apply to the 13-year-old now in custody however. Moeller, the prosecutor, said juvenile cases typically don’t result in a felony charge that remains on the defendant’s records. Cases transferred to adult court typically involve a defendant who is 16 or older and who has committed murder, rape or assault, Moeller said.

It’s unclear whether the 13-year-old had any mental health issues, or any treatment for them before arrest. Thompson said he didn’t know.

The boy had no prior run-ins with police, however, the chief said.

Around 1 p.m. Monday, Thompson reported that there had been another arrest of a student Monday at the school. That arrest, of a student Thompson said had either autism or a mental health issue, wasn’t related to the social media post over the weekend, Thompson said. He said the arrest was due to something school officials interpreted as a threat.

“Since Parkland, everybody has been zero tolerance for anything that sounds like violence,” Thompson said.

​Staff writer Kirsten Fiscus: 256-235-3563. On Twitter @kfiscus_star.