WASHINGTON (JTA) — A Washington, D.C., white supremacist was arrested on a gun charge after family members warned police that he said the Pittsburgh synagogue killings last month were a “dry run.”

Jeffrey Clark, 30, appeared Tuesday in U.S. District Court on charges of illegally possessing a firearm and a high-capacity magazine, The Washington Post reported.

Two family members alerted police after Clark grew increasingly agitated in the wake of the suicide of his 23-year-old brother, Edward, on Oct. 27, just hours news broke of the worst anti-Jewish attack in U.S. history, when a gunman killed 11 worshippers at The Tree of Life synagogue complex in Pittsburgh.

The brothers were active on far-right social media. Jeffrey Clark had been “friended” by the alleged Pittsburgh gunman, Robert Bowers, on the far-right chat site Gab.

Huffington Post reported that Jeffrey Clark wrote on Gab that the Pittsburgh killings were a “dry run” and “the f***ing kikes that got shot by the hero #RobertBowers were all active supporters of pedophilia … and every last one of them deserved exactly what happened to them and so much worse.”

Conspiracy theories linking hated figures to child abuse are commonplace on the far right.

Huffington Post reported that photos showed Jeffrey Clark at the neo-Nazi rally in Charlottesville, Virginia, in August 2017. The rally included violence against counterprotesters and culminated in a deadly car ramming that killed one counterprotester and injured at least 20.