Police and school officials are accusing two Eugene teenagers of paying a third party to make four bomb threats against South Eugene High School in May.

Eugene Police Department Chief Chris Skinner said Wednesday that two South Eugene High students found the anonymous third party on the social media platform Telegram, and that an employee of the Eugene School District tipped off police after spotting an Instagram post that linked to a Telegram user who offered to send threats for a fee. It’s not clear what either post said or who made them; police did not specify.

On May 3, May 10, May 16 and May 24, Eugene police received bomb threats at South Eugene High School through calls to 911. The callers claimed to be inside the school armed with explosives in each instance, and armed with a gun in some. Each time, police responded, put the school on lockdown and then determined the threats weren’t credible.

“It was mostly a hoax, but nonetheless, it’s scary,” Skinner said. “It’s scary for staff. It’s scary for students. It’s scary for our community.”

Once police learned of the third party, they enlisted the FBI.

Other news outlets, including the Associated Press, have linked false threats against schools to “swatting,” the act of making a fictitious report of an emergency, or a threat of violence, with the expectation that armed police officers will respond. The tactic has been used to harass celebrities and others in their homes and offices.

On Tuesday, police and the FBI acted on a search warrant and seized personal electronic devices. They did not say what or where exactly.

Police in Eugene have forwarded details of their investigation to the Lane County District Attorney’s Office for possible prosecution, Skinner said Wednesday. The two accused students remain in the custody of their parents who are cooperating with the investigation. Skinner declined to release the students’ names, ages, grades and genders.

Skinner said the FBI will continue to investigate who is behind the third-party service.

All four of the threats appeared to have been made using a computer generated voice, said Eugene Police Department spokesperson Melinda McLaughlin.In recent months, the use of an automated voice has been linked to swatting incidents around the country. The Educator’s School Safety Network, a nonprofit that tracks incidents of school-based violence and threats, reports over 430 swatting calls targeting schools this year. Skinner said IP addresses and the automated voice linked to the threats in Eugene, have appeared in similar cases across Oregon and nationally, in states such as Texas and Tennessee.

“I sympathize with every parent at South Eugene High School,” district Superintendent Andy Dey said. “I have two children that have been there for every one of those last four episodes and I know exactly what it’s like to wonder whether or not your child is in danger.”