The teenager made two threats on Snapchat, each followed with a smiley face and bomb emoji; he could face 10 years in prison.
Jesus Castrodad, 49, and his 32-year-old girlfriend Colleen Kasdaglis were allegedly caught on Nov. 6, shortly after what authorities allege was placing what may have been their seventh bomb threat to the courthouse.
Michael Kadar, 19, began making hoax threats when he was still a minor and claimed it was "like a game" for him.
After the Parkland, Florida, school shooting, school violence incidents have increased dramatically.
The U.S. Secret Service was already familiar with the man.
A shooting survivor urges Americans to stand firmly against the NRA's "guns everywhere, for anyone, no questions asked" agenda.
Threats were phoned in or emailed to JCCs in states including New York, Wisconsin, Illinois and Florida overnight and early on Tuesday.
No one claimed responsibility for the calls on Wednesday nor nine days ago, and the Federal Bureau of Investigation (FBI) has not named any suspects nor described a likely motive.
Los Angeles Unified School District closed all their schools and campuses.
Hungarian authorities declined to rule out that ISIS militants were involved.
Two of the four buildings that were evacuated after an "unconfirmed bomb threat" have reopened.