Following his arrest, Holzer waived his right to remain silent and admitted to planning to blow up Temple Emanuel synagogue, the court documents said.

He allegedly told an undercover Federal Bureau of Investigation agent that he hoped to poison members of the synagogue and claimed he had paid off a "Mexican cook to hex and poison" attendees by putting arsenic in the water pipes, according to an arrest affidavit.

An undercover agent posing as a white woman who shared Holzer's ideology friended him on Facebook Sept. 28 and he told her he was a former Ku Klux Klan member-turned-skinhead, the docs say.

Atlas-Acuna said the synagogue has a security plan in place for these types of events.

According to the affidavit, when asked what if people were in the building when the bomb exploded, "Holzer stated that he did not think anyone would be there, but that if they were, Holzer would not care because they would be Jews".

According to court documents, Holzer claimed that he had previously hired a man nicknamed "Mexican Hitler" for $70 to "hex and poison" the synagogue by putting arsenic in its pipes. Once he arrived at the motel, the undercover agents showed him the pipe bombs, to which Holzer responded, "This is absolutely gorgeous".

A white supremacist plotted to bomb a Colorado synagogue as part of what he called a "racial holy war" federal authorities said Monday.

Holzer allegedly visited Temple Emanuel multiple times after he hatched his plot with the undercover agents.

At Holzer's 2 p.m. court appearance, the judge read the charge against him and said Holzer would be held without bond pending his next court appearance, which is set for November 7.

The sting operation into Holzer began in September when an undercover agent reportedly got in contact with him through Facebook.

Holzer has been charged with intentionally attempting to obstruct persons in the enjoyment of their free exercise of religious beliefs, through force, and the attempted use of explosives and fire.

"You're not going to make us cower in fear, and we're not going to just be sheep and go to the slaughter", congregant Helena Atlas-Acuna said.

Holzer made his first appearance in Denver federal court on Monday afternoon.

"Holzer repeatedly expressed his hatred of Jewish people and his support for... a racial holy war", the U.S. attorney's office for Colorado said in a statement.

The Temple Emanuel, a Reform Jewish synagogue, opened in 1900.

It has a congregation of about 30 families and a rabbi from Denver who travels to Pueblo twice a month.

Holzer's arrest comes as Jewish institutions around the country are still reeling from the mass shooting last October at Pittsburgh's Tree of Life synagogue.

"Mr. Holzer will now have the opportunity to explain his behavior through our court system in a constitutional way", Davenport said, "which, in the spirit of irony, protects religious freedom as one of its most golden rules". A voicemail left at the temple wasn't immediately returned.