A man who authorities said was arrested Friday for making a series of recent threats against Jewish Community Centers in an attempt to vilify his ex-girlfriend is a former journalist who was fired from a publication for falsifying stories.

Juan Thompson was arrested Friday in St. Louis and charged with one count of cyberstalking. Authorities said he is believed to have made at least eight threats against Jewish Community Centers and the Anti-Defamation League in recent months, a handful of the more than 100 threats currently under investigation so far this year.

“The defendant allegedly caused havoc, expending hundreds of hours of police and law enforcement resources to respond and investigate these threats,” said New York City Police Commissioner James P. O’Neill. “We will continue to pursue those who peddle fear, making false claims about serious crimes.”

Mr. Thompson had previously worked for the online news organization, The Intercept, but was fired in 2016 after the outlet discovered he had fabricated sources and quotes in several of his articles.

According to prosecutors, Mr. Thompson began harassing his ex-girlfriend after they broke up in July 2016, initially by pretending to be from a news organization and contacting her employer to say that she had been pulled over for drunken driving. The harassment escalated over the next several months, with the 31-year-old making a report to the National Center for Missing and Exploited Children that his ex-girlfriend was in possession of child pornography, according to a federal complaint filed in court.

When police contacted Mr. Thompson about the claim, he denied making it and said his email had been hacked, the complaint states. He was warned by police to stop harassing his ex-girlfriend, who by that point had taken out a protective order against him.

In January and February, as authorities were investigating a series of bomb threats made against Jewish Community Centers across the country, authorities said Mr. Thompson began making threats to several centers. Prosecutors believe he is responsible for at least eight of the threats, including a bomb threat made against the Anti-Defamation League’s headquarters in New York on Feb. 22.

The Anti-Defamation League said Mr. Thompson was on the radar of their Center on Extremism on account of his prior falsification of articles during his time at The Intercept.

One story fabricated by Mr. Thompson was about Dylann Roof, the white gunman who killed nine black churchgoers in Charleston, South Carolina. The story, which was later retracted by The Intercept, stated that Roof had previously been dumped by his girlfriend for a black man.

“Most recently, Thompson allegedly announced in November 2016 that he was running for mayor of St. Louis, to ‘fight back against Trumpian fascism and socio-economic terrorism,’ ” the ADL said in a statement Friday. “According to ADL research, Thompson also claimed that he wanted to dismantle the system of ‘racial supremacy and greedy capitalism that is stacked against us.’ He created a Gofundme page to raise $5,000 for his ostensible election bid. He got $25. He has tweeted various rants against white people, calling them ‘trash’ and saying they ‘have no shame.’”

Jonathan A. Greenblatt, the CEO of the Anti-Defamation League, said the organization was “received and gratified” by news of the arrest. The Intercept confirmed in a statement Friday that Mr. Thompson had previously worked at the news outlet.

“We were horrified to learn this morning that Juan Thompson, a former employee of The Intercept, has been arrested in connection with bomb threats against the ADL and multiple Jewish Community Centers in addition to cyberstalking,” said managing editor Charlotte Greensit. “These actions are heinous and should be fully investigated and prosecuted.”