The anniversary of the Columbine massacre is believed to be the inspiration for vague threats of violence circulated by Petaluma students on social media, a school district spokesman said Thursday.

Petaluma police have now deemed the threat not credible and stated there is no active threat at Petaluma schools. A Casa Grande High School student was arrested for allegedly making the threats and is in police custody, said Petaluma police Lt. Dan Fish.

A post on Snapchat Wednesday evening warned of shooting that would occur at Casa Grande High School in Petaluma.

Police made a number of home visits Wednesday night to teenagers who had been involved in reposting them, said David Fichera, communications coordinator for Petaluma City Schools.

School administrators sent an email to parents of all high school students Thursday morning, alerting them to the investigation.

The massacre at Columbine High School in Colorado occurred April 20, 1999. Two students killed 13 people before killing themselves.

You can reach Staff Writer Paul Payne at 707-568-5312 or paul.payne@pressdemocrat.com. On Twitter @ppayne.