A Washington, D.C., man suspected of being a white nationalist and befriending the Tree of Life synagogue gunman on a social media platform before the tragedy is under arrest for firearms charges in the District.

Jeffrey Clark Jr. is charged with illegal possession of high-capacity firearms magazines and unlawful guns and is scheduled to appear in court Friday for a detention hearing.

An FBI affidavit says Clark admitted that he was a member of white nationalist groups and told investigators he had contact with the Pittsburgh Tree of Life synagogue shooter on social media, praising him as a hero. The affidavit says Clark connected with Robert Bowers on Gab, a social networking site. According to the affidavit, Clark openly discussed killing people of the Jewish faith, as well as African Americans. The affidavit said Clark spoke about Bowers, claiming the synagogue shootings were “justified,” because a same-sex “Jewish couple was having an adopted baby circumcised that week.”

According to the FBI affidavit, witnesses said Clark attended the 2017 “Unite the Right” rally in Charlottesville and was photographed standing next to James Alex Fields, a white nationalist who prosecutors say drove a car into a crowd of counter-protesters, killing one.

The affidavit also cites social media posts by Clark, including one with vulgar language, calling Bowers “a hero” and saying victims at the synagogue “deserved exactly what happened to them and so much worse.”

Clark's family took his guns and reported him to the authorities, according to the FBI.

“I'm so very grateful that they took the courageous step to turn him in but I cannot imagine just the inner turmoil of giving up your own child,” a neighbor of the Clarks said.

In their court filings, federal agents said they obtained four boxes of gun parts from Clark.

“Agents recognized several items in the boxes as parts used to modify AR-15 assault rifles,” the affidavit said.

Agents said they also recovered AR-15 rifle conversion kits and four high-capacity AR-15 magazines capable of holding up to 30 rounds of ammunition, according to the affidavit.

Clark’s attorney did not immediately return requests for comment.

Jeffrey Clark Sr. had no comment about his son’s arrest.

A neighbor said she’s lived in the Bloomingdale neighborhood for 15 years and knows the Clark family well but didn’t have any idea about alleged ties to white nationalists.

“It’s demoralizing; it’s depressing,” she said. “The existential angst is tremendous. It’s very hard to deal with.”

Bowers and the Tree of Life shooting are being investigated by federal officials in Pittsburgh. In a statement to the I-Team, a spokeswoman for the US Attorney for the Western District of Pennsylvania said: “As previously stated by both the US Attorney’s Office of Western District of Pennsylvania and Special Agent in Charge of the Pittsburgh Office of the FBI, there is currently no evidence that any other individuals were involved or hard prior knowledge of the Tree of Life synagogue attack. That statement remains true.”