An Israeli court convicted a 19-year-old man on Thursday in connection with threats made against organizations and individuals around the world, including the Israeli Embassy in Washington and numerous Jewish groups in the United States.
The youth court withheld the man’s name because some of the crimes were committed before he was an adult, but the Justice Department identified him, in charging documents last year and indictments this year, as Michael Ron David Kadar, a dual American and Israeli citizen.
In the verdict, Judge Zvi Gurfinkel of the Tel Aviv district youth court said that the man had threatened thousands of people between 2015 and early 2017 “with acts of terror and murder that would be executed in an area filled with people, and that these acts would be executed by explosion or shooting and would harm many.”
The targets included “airlines, airports, schools, malls, police stations, hospitals” and other institutions, he said.
Mr. Kadar was arrested in Israel on March 23, 2017, after months of making threats against Jewish institutions, the authorities say. The threats raised fears of growing anti-Semitism in the United States.
His lawyer had argued at the time that Mr. Kadar, who was born in Israel, had developed a brain tumor when he was 14 years old that affected his behavior. Although Judge Gurfinkel did not address the tumor in his verdict on Thursday, he did say that Mr. Kadar was fit to stand trial despite having received an autism diagnosis.
The judge convicted Mr. Kadar of “all the crimes attributed to him” since he turned 18 on Aug. 25, 2016. It was not immediately clear when Mr. Kadar would be sentenced or how severe the sentence would be.
According to the American documents, Mr. Kadar made threats against Jewish community centers, schools and historic institutions, as well as the Anti-Defamation League’s offices in Washington and New York. Mr. Kadar made at least 245 threatening phone calls in the first two months of 2017 alone, according to the F.B.I.
The phone calls to groups and institutions often warned of bombs in the building or an impending mass shooting. The threats were taken seriously, resulting in evacuations, lockdowns and the closing of buildings and offices.
In a call in February 2017 to a Tampa Jewish Community Center preschool, for example, Mr. Kadar warned of a bomb that would blow off the heads of the “Jew children” there, according to the charging documents filed last year, which described the F.B.I. investigation.
Mr. Kadar was also accused of engaging in “swatting,” the practice of calling the police with dramatic, but false, reports intended to provoke a large and potentially dangerous law-enforcement response.
Using multiple digital tools, Mr. Kadar was able to mask his identity, alter his voice, hide his phone number and reroute his internet traffic through intermediaries, according to the charging documents.
After issuing more than 100 subpoenas to assorted technology companies, the F.B.I. traced the calls to Israel. The authorities there narrowed the search to a neighborhood in Ashkelon, a small city where they arrested Mr. Kadar.
Unprompted, he told the authorities that he “did not do” the “JCC threats,” according to the documents. On his laptop, they found recordings of calls arranged into folders bearing names such as “Bomb Threats to Jewish Institutions Feb 27 2017.”
In February, the Justice Department announced that Mr. Kadar had been indicted in the District of Columbia, Georgia and Florida on dozens of charges related to the calls, including hate crime charges, each carrying a maximum penalty of 20 years in prison, and multiple bomb threat charges, each carrying a penalty of up to 10 years in prison.
Myra Noveck contributed reporting from Jerusalem.