A 15-year-old Florida boy was arrested after posting a message on Instagram threatening to kill people at several Broward County schools, authorities said.

Just after midnight Friday, Broward Sheriff's Office detectives were notified about the online post from a Fort Lauderdale teen. He posted it one day after 17 people were killed during a mass shooting at Marjory Stoneman Douglas High School in Parkland.

The teen told detectives that the post was a joke aimed to scare his cousin and he appeared remorseful, according to a sheriff's news release.

The juvenile is facing one count of sending a written threat to kill, which is a third-degree felony.