The Paris prosecutor’s office is investigating a hoax hostage alert that prompted a major police intervention at a church in the center of the French capital.

Police dispatched a helicopter and barricaded the area around the Saint-Leu church in the Les Halles neighborhood Saturday, and activated a special app-based public alert system created after deadly attacks in Paris last year. The Interior Ministry later said it was a false alarm.

The prosecutor’s office said Monday that an investigation is under way, and the perpetrators are still at large.

Obs magazine reported that it had reached two people who boasted online of staging the hoax in a case of so-called “swatting,” when hoaxers make anonymous threats to trigger a response from police and SWAT teams.

(AP)