Investigators believe that Roy Den Hollander, the self-proclaimed "anti-feminist" lawyer accused of fatally shooting the son of a federal judge and wounding her husband, may be responsible for the murder of a men's rights activist in California earlier this month.

"As the FBI continues the investigation into the attack at the home of U.S. District Court Judge Esther Salas, we are now engaged with the San Bernardino CA Sheriff’s Office and have evidence linking the murder of Marc Angelucci to FBI Newark subject Roy Den Hollander," the FBI said in a statement. "This investigation is ongoing."

On Sunday, a man wearing a FedEx uniform walked up to Judge Salas's North Brunswick, New Jersey home and rang the bell around 5 p.m. Her 20-year-old son, Daniel Anderl, answered the door and was fatally shot in the chest, while her husband, Mark Anderl, who was near the front door, was shot multiple times. Salas, who had been in the basement, was unharmed; Anderl remains hospitalized.

Den Hollander was found dead on Monday, in his Rockland County home, of self-inflicted gunshot wounds. Authorities say he was in possession of a photo of New York Chief Judge Janet DiFiore, prompting Governor Andrew Cuomo to order protection for her.

Den Hollander was an outspoken provocateur, who filed numerous lawsuits claiming discrimination against men (like against bars' "ladies' night" promotions) and also posted virulent misogynistic and pro-Trump screeds, including one that imagined raping the female judge involved in his divorce case.

Angelucci was killed on July 11th in Crestline, by a man wearing a FedEx uniform. He had been the vice president of the National Coalition for Men.

According to the Daily Beast, "Den Hollander had once been a member of the National Coalition for Men (NCFM), the organization where Angelucci volunteered, until he was drummed out. The two men had filed dueling lawsuits, challenging the military’s male-only draft policy, on opposite coasts. But while Angelucci scored a huge win in his case in February, Den Hollander’s was still pending in New Jersey—in Salas’ courtroom."

"All of this misogynism is fundamentally about repressing women and subjugating women against their will," said John Horgan, a Georgia State University professor, an expert in extremist groups, told NBC News. "These men are so deeply insecure and are fueled by this fundamental inability to cope with women progressing in today’s world.”

Harry Crouch, president of NCFM, spoke to KCAL mourning Angelucci's death. He also said of Den Hollander, "I immediately saw a link, [between the killings]. But I want to be real clear, he’s not a NCFM member. Why isn’t he? Because I threw him out five or six years ago, because he was a nut job.”