The San Bernardino County Sheriff's Department said Angelucci was killed at his home in Crestline, California, not far from Los Angeles. Angelucci was an attorney and men's rights activist. The FBI is currently investigating the murder.

Authorities are investigating any possible connections between Den Hollander, the men's rights attorney suspected of shooting a federal judge's family on Sunday, and the murder of another men's rights activist in California last week, according to a law enforcement source.

More than a week after Angelucci was killed, US District Judge Esther Salas's husband was shot, and her son was killed in an attack at her home. Den Hollander, who authorities have identified as the primary suspect in that attack, was found dead less than 24 hours later of what officials believe was a self-inflicted gunshot wound.

Den Hollander was also an attorney who claimed to be part of the men's rights movement and described himself as "anti-feminist."

Paul Elam is a friend of Angelucci and fellow men's rights activist who said he believes Den Hollander harbored a grudge against Angelucci for years because they both represented cases that contested the selective service registration only applying to men, saying it was discriminatory.

"Roy was furious and beyond words furious, absolutely enraged that (the National Coalition for Men) and Marc Angelucci were getting into the selective service case. He viewed that as something proprietary for him," Elam said on a Facebook live video Monday night. "He saw Marc's work in that respect as an intrusion into his space. He was more than angry about it, he was livid."

Elam said in the video that he did not know if Den Hollander made any threats against Angelucci. CNN has attempted to contact Elam for further comment.

Both Elam and Angelucci are members of the National Coalition for Men, a group that the Southern Poverty Law Center mentions in a list of "extremist" ideologies and figures, and points to Elam's written beliefs that men are superior to women.

When asked to comment on the SPLC listing it as an extremist group, NCFM president Harry Crouch said that Elam was a close personal friend but his views on male supremacy were not held by the group, and that the group rejects the concept of male supremacy.

Cassie Jaye, a friend of Angelucci, said he approached the men's rights movement differently than Den Hollander, and was not anti-women. Jaye made a documentary about the men's rights movement that featured Angelucci.

"When he was litigating on behalf of men's issues, he was still always considering the female plight and perspective," Jaye told CNN. "He was just a great guy and well-loved within the men's rights community."

National Coalition for Men kicked Den Hollander out

Harry Crouch, president of the National Coalition for Men, tells CNN he kicked Den Hollander out of the group after Den Hollander called and threatened him around December 2015.

Crouch says Den Hollander wa