Domestic terrorism and hate crimes have become a growing concern for law enforcement in recent years as a number of high-profile attacks have left scores dead across the country. Eleven worshippers were killed in October last year when a white supremacist opened fire at the Tree of Life synagogue in Pittsburgh.
Holzer first came on the FBI's radar after a tip in late September regarding comments he'd made online "of concern indicating a possible threat to the community," FBI Denver Special Agent in Charge Dean Phillips said at a news conference.
"This case emphasizes our continued efforts to aggressively and promptly address threats to our community to include violence against places of worship. I cannot stress enough the importance of reporting threats in our neighborhoods," Phillips said.
Undercover FBI agents approached Holzer online soon after the tip and were interacting with him as he allegedly plotted the attack on Temple Emanuel. In a meeting with three undercover agents at a restaurant in Colorado Springs last month, Holzer proposed using Molotov cocktails to destroy the Pueblo synagogue, according to the complaint.
"I want something that tells them they are not welcome in this town," Holzer allegedly said. "Let's get that place off the map."
Temple Emanuel Congregation President Michael Atlas-Acuña told CNN the small Jewish community of about 35 families hasn't had any similar threats in the past.
"The Pueblo community has embraced the Jewish community and we've never had any kind of threats or vandalism or anything like this," Atlas-Acuña said. Holzer, he said, is a "transplant" and not from Pueblo.
The synagogue has had security guards, though, for the past few years, after shootings in other places, he said, and a sign in front states it isn't a gun-free zone, Atlas-Acuña said.
"I think it's stupid for people to put signs up that say this is gun-free zone," he said. "Like advertising. They're hitting soft targets and churches, and synagogues are soft targets."
The temple is 119 years old and on the National Register of Historic Places, Atlas-Acuña said. It's never been closed for any reason, and services will be held as usual after this week's threat.