The co-conspirators in the plot turned out to be undercover agents, who arrested the man shortly before he planned to bomb the synagogue early Sunday morning, according to court documents.
Richard Holzer was arrested Friday in Pueblo just after the agents brought him what he believed were two pipe bombs along with dynamite to blow up Temple Emanuel. In fact, the undercover agents had phony bombs incapable of causing damage, authorities said.
Holzer, 27, described what he thought were the explosives as "absolutely gorgeous" and said they should go ahead with the attack overnight to avoid police, the court document said.
Holzer, who lives in Pueblo, was due to make his first court appearance Monday. A message left with Julia Martinez, a public defender assigned to represent Holzer, was not immediately returned.
The foiled plot is the latest attempted attack against a synagogue in the U.S. just over a year.
In October 2018, a shooting at the Tree of Life synagogue in Pittsburgh killed 11 people and became the deadliest attack on Jews in U.S. history.
In April, a woman was killed, and three people were injured when a man opened fire inside a Southern California with an AR-15 military-style rifle.
The investigation into Holzer began after an undercover FBI agent purporting to be a woman who supports white supremacy contacted him on Facebook.
Holzer repeatedly espoused anti-Semitic and white supremacist views in his messages with the agent. "I wish the Holocaust really did happen...they need to die," he wrote her on Facebook, according to the court documents.
Holzer told the agent he had checked out the temple property and met with her and other undercover agents at a Pueblo motel on Friday. He brought a copy of Adolf Hitler's "Mein Kampf" with him, the documents said.
The agents then arrested Holzer, who waived his right to remain silent and spoke to investigators, the documents said.
"He referred to the plan as 'my mountain' and to Jews and Synagogues as a 'cancer' to the community," the document said.
He also told agents he didn't want to hurt anyone but would have proceeded with an attack if he knew someone was inside, the papers said.
U.S. Attorney Jason Dunn in Denver and FBI Denver Division Special Agent in Charge Dean Phillips planned a news conference Monday.
The Temple Emanuel synagogue is the second-oldest in Colorado and was completed in 1900, according to Temple Emanuel's website.
It has a congregation of about 30 families and a rabbi from Denver who travels to Pueblo twice a month. Pueblo is about a two hour drive south of Denver. A voicemail left at the temple Monday afternoon wasn't immediately returned.