The man, identified as Richard Holzer, 27, used several Facebook accounts to "promote violence and show support for the Holocaust", the authorities said.
Federal authorities in Colorado have arrested a white man they accused of plotting to blow up a synagogue in Pueblo, a city two hours south of Denver, according to federal court documents.
The man, identified as Richard Holzer, 27, used several Facebook accounts to "promote violence and show support for the Holocaust", writing in July in a private message, for example, that he was "getting ready to cap people," the documents said.
The message included a picture of him aiming a long gun while dressed in clothing displaying white supremacy symbols. He told another Facebook user, "I wish the Holocaust really did happen" and, speaking of Jews, "they need to die."
Mr. Holzer was arrested on Friday after he was first contacted by an undercover F.B.I. agent in September. It is not clear when investigators began tracking him or how they were first alerted to his posts. Speaking over Facebook Messenger shortly after contact was made, he told the agent he was formerly a member of the K.K.K. and now identified as a skinhead.
If convicted of "attempting to obstruct religious exercise by force using explosives and fire", Mr. Holzer faces up to 20 years in prison.
In October, according to the court filing, Mr. Holzer told the undercover F.B.I. agent that he was going to scope the synagogue and sent the agent a video from outside. He then told the agent his plan was to poison members of the synagogue on Oct. 31, possibly with arsenic. He invited the agent to join him.
Later, Mr. Holzer and a friend identified in the documents as Skeeter met with three undercover F.B.I. agents, with whom he began to discuss alternate plots, including a plan to build Molotov cocktails and weld the temple doors shut. Mr. Holzer stated that he wanted to "vandalize the place beyond repair," the documents said. He then visited the synagogue with the agents, where Mr. Holzer assessed that the Molotov cocktails would not be enough.
The agents "offered to supply" pipe bombs, according to the documents. Several days later, Mr. Holzer met the agents to pick up the bombs, which were inert, according to officials. Authorities arrested him shortly after, and he admitted that he had been planning to blow up a synagogue in the middle of that night.
Officials said he referred to the plan as "my mountain" and to Jews and the synagogue as a cancer to the community.
Mr. Holzer’s arrest marks the 13th time since the Pittsburgh attack that authorities have apprehended someone for allegedly plotting attacks or making threats against a Jews, according to a report from the zionist supremacist Anti-Defamation League.
The zionist organization had been tracking Mr. Holzer’s online activity since May 2016, according to Scott Levin, its regional director, and had repeatedly shared information with law enforcement, citing a concern that "he might pose a threat to public safety".