ROCKFORD, MI -- A 16-year-old Rockford High School student who faces criminal charges for his alleged involvement in ongoing bomb threats toward the district does not have a prior criminal record, authorities said.

Police announced Wednesday, June 17, the Belmont teen faces a charge of false report or threat of terrorism, a 20-year felony. Officials from the sheriff's department, FBI, Rockford Department of Public Safety and Rockford Public Schools are expected to speak about the case at a Thursday morning press conference.

A court supervisor has been told a plea agreement is in the works.

The district received at least a half dozen threats in the form of phone calls, emails and social media messages since October. The anonymous threats prompted lockdowns while police and bomb-sniffing dogs searched school buildings. All 1,900 high school students were evacuated on one occasion.

Kent County Undersheriff Michelle Young said authorities plan to seek restitution. That amount was not finalized Wednesday.

Young declined to say how investigators tracked the teen, but court records show police sought search warrants for IP addresses and records for at least eight Twitter accounts when investigating the bomb threats.

The teen worked with others who lived out of state, Young said.

On Jan. 15, the Rockford dispatch center received a call at 12:04 p.m. from a California number that was traced to a free voice-over-Internet program. A robotic, digitized voice made a statement along the lines of "going to blow up the school in 20 minutes, I have a propane bomb in a duffel bag in a classroom," a detective wrote in a search warrant affidavit. The threat was directed at the high school.

The following day, the dispatch center received another threat from a different number about 12:45 p.m. A similar digitized voice told the dispatcher he would drive a vehicle into the Freshman Center on the high school's campus and if the explosives didn't work, he would "start shooting people," documents state.

Around that time, school employees notified police that the district Twitter account, RAMpridenews, was receiving tweets from a user who said they knew who was responsible for the bomb threats. Police said that Twitter user had talked about swatting in the past.

A few additional Twitter users sent threats to the district's social media account. Their tweets talked about blowing up the high school and putting nerve gas in the air ducts, as well as personal threats to "assassinate" Superintendent Michael Shibler, according to court documents.

The Twitter threats continued into mid-February, when a series of death threats made references to a Columbine-style attack while naming eight or nine students. A Twitter user claimed to be responsible for the phone and email threats. The person taunted the district and Shibler and said, "I hope you all die from a bomb."

Court records show the various Twitter conversations showed an apparent link to harassing phone calls to a Rockford family that started around the time the bomb threats began.

Angie Jackson covers public safety and breaking news for MLive/The Grand Rapids Press. Email her at ajackso3@mlive.com, and follow her on Twitter.