Investigators believe one person is behind a large number of the threats made against US Jewish institutions in 2017, New York City's head of police intelligence says.
John Miller told TV show CBS This Morning on Thursday the threats were co-ordinated and a man using a voice changer was behind them.
They also thought he was using a phone spoofing device that made it appear the call was not from the number he was using.
The Anti-Defamation League says 148 threats targeting Jewish institutions have been received across the country since January.
A Jewish children's museum in Brooklyn was evacuated for a few hours on Thursday after police investigated an emailed bomb threat.
