On Monday, FBI Director Christopher Wray confirmed that one person is believed to be responsible for a majority of the bomb threats made to HBCUs earlier this year.

Wray said that the bomb threats were linked to a sole unidentified juvenile who has been prosecuted as a minor by state authorities.

“We’ve recently — with respect to the first big tranche of the threats — the investigation has identified an underage, a juvenile subject. And because of the federal limitations on charging juveniles with federal crimes, we have worked with state prosecutors to ensure that that individual is charged under various other state offenses, which will ensure some level of restrictions and monitoring and disruption of his criminal behavior,” Wray told lawmakers on the House Homeland Security Committee.

The surge in bomb threats started on Jan. 5, when Howard University and seven other historically Black institutions were targeted. By February, 17 different HBCUs had received threats, The Hill reports.

The FBI said the bomb threats had been made in phone calls, emails, instant messages, and anonymous online posts.

Federal investigators initially identified six “tech savvy”  juveniles as persons of interest in the case back in February. According to USA Today, this prompted a wide-ranging inquiry involving at least 30 of the FBI’s 56 field offices, but later linked the communications to one person.

Wray said the suspect in custody is being investigated for one string of calls, but they are still investigating other threatening calls made to HBCUs.  

USA Today reports that the investigation is continuing into two other tranches of threat streams: one involving 19 racially-motived communications between Feb. 8 and March 31, that have since been linked to Internet addresses abroad.

“Since that big tranche that we believe that individual was responsible for, there have been two other tranches. And we’re very actively investigating those, but there’s not much I can say on those ongoing active investigations, those other investigations, at this time” Wray said.