A white supremacist has been arrested for plotting to blow up a synagogue in Colorado.

Richard Holzer, 27, was charged for planning to attack Temple Emanuel, a congregation in Pueblo of 35 families whose building dates to 1900.

According to an affidavit describing the charges, Holzer is a self-described “skinhead” and former Ku Klux Klan member who has used Facebook to “promote white supremacy ideology and acts of violence.”

The affidavit describes weeks of undercover work by the FBI leading to Holzer’s arrest on Friday, beginning with an undercover agent making first contact with Holzer online in September. Holzer told the agent he was preparing for a “RAHOWA,” or racial holy war.

In mid-October, Holzer met for the first time with FBI agents posing as white supremacists and discussed his plan to blow up the synagogue. He also gave them white supremacist paraphernalia, including a flag, patches and a mask.

Holzer also claimed to have enlisted a Mexican ally in a scheme last year to poison the synagogue’s water supply with arsenic — he said it led to the synagogue being shut down. But Helena Atlas-Acuna, the synagogue’s board secretary, said the water supply was not, in fact, poisoned.