Police say they’ve arrested a student they believe was responsible for sharing a photo of guns on social media with writing that warned people not to come to a Long Beach high school.

The picture, which appeared to be posted to Instagram, showed several rifles with the text “Don’t go to Millikan tomorrow” written over them, apparently referring to Millikan High School in East Long Beach.

Police said the post was made on a female student’s account. Shortly after it was posted, there was another post saying essentially that the post was a joke or the student’s account had been hacked, LBPD officer Ben Hearst said.

Nevertheless, police investigated to make sure the ominous post wasn’t a legitimate threat, according to authorities.

Police were notified of the post around 5 p.m. Monday and by 10:30 p.m., the department said they’d made an arrest and determined Millikan was safe.

“At this time, the department is confident there is NO threat to the high school,” police said.

The Long Beach Unified School District told parents that Millikan will operate as usual on Tuesday, “though you may see additional police patrols deployed around the campus.”

Editor’s note: This story was updated with more information from police and the school district.