American Jewish groups said they were simultaneously relieved and anguished at the news Thursday that authorities had arrested a young Israeli man for making threats to Jewish schools and facilities in recent months.

While the groups – some of which received bomb threats – praised law enforcement for making an arrest, they also expressed sadness after learning that authorities believed a 19–year–old Jewish man is behind most of the threats.

“It was heartbreaking to learn that a Jewish man is a prime suspect,” Jerry Silverman, president and chief executive of the Jewish Federation of North America, said.

The stream of bomb threats to U.S. schools and institutions have helped fueled heightened anxiety about anti-semitism and forced repeated evacuations of Jewish Community Centers, offices, daycares and school buildings.

The Anti–Defamation League said that as of this week, there had been 166 threats made in 38 states as well as three Canadian provinces, a tally that included threatening messages sent to five ADL offices.

“While the details of this crime remain unclear, the impact of this individual’s actions is crystal clear: These were acts of anti-semitism,” Jonathan Greenblatt, chief executive of the ADL, said in a statement. “These threats targeted Jewish institutions, were calculated to sow fear and anxiety, and put the entire Jewish community on high alert.”