The two killings on opposite sides of the country were strikingly similar. A gunman showed up at the front door, posing as a delivery man, and opened fire.
One of the victims was Marc Angelucci, 52, a men’s rights lawyer who was killed on July 11 outside his home in San Bernardino County, Calif. Eight days later, a shooter approached the New Jersey home of Esther Salas, a federal judge, killing the judge’s son and leaving her husband seriously injured.
On Wednesday, the F.B.I. office in Newark said in a statement that agents had uncovered evidence linking Mr. Angelucci’s killing to Roy Den Hollander, who is also the primary suspect in the New Jersey shooting.
It was the first time that the authorities had publicly connected the two killings.
Mr. Den Hollander, 72, was found dead in the Catskills in New York on Monday in an apparent suicide, hours after the shooting at Judge Salas’s home. He was a self-described anti-feminist lawyer who wrote thousands of pages in online screeds denouncing women, including female judges.
On Wednesday, the F.B.I. did not publicly say what evidence had been uncovered. But the authorities investigating Mr. Den Hollander’s apparent suicide found a semiautomatic Walther pistol that was of the same caliber as the weapon used in both the California shooting and the New Jersey shooting, according to a law enforcement official briefed on the matter.
Investigators were conducting ballistics tests to determine whether that weapon was used in both attacks, according to law enforcement officials.
The authorities are investigating whether Mr. Den Hollander was seeking revenge against his enemies after receiving a terminal cancer diagnosis, according to a different law enforcement official. In a self-published book last year, Mr. Den Hollander said he learned in late 2018 he had a rare form of melanoma.
Although Mr. Den Hollander detailed extensive grievances against judges and others in his online writings, it was not clear whether he was planning more violent attacks.
The F.B.I. has contacted New York State’s chief judge, Janet M. DiFiore, to notify her that Mr. Den Hollander had her name and photo in his car, according to her spokesman, Lucian Chalfen.
The name of another female state judge, who presided over a case that Mr. Den Hollander was involved in, was also found in his car, Mr. Chalfen said. He declined to name the judge.
Mr. Den Hollander’s connection to Judge Salas and Mr. Angelucci revolved around the same case.
In 2015, Mr. Den Hollander brought a legal challenge to the male-only military draft that was assigned to Judge Salas in Newark federal court. Two years earlier, Mr. Angelucci had filed a similar lawsuit in a different jurisdiction.
In February 2019, a federal court in Houston ruled in Mr. Angelucci’s favor, finding that the exclusion of women from the draft was unconstitutional. The case is now on appeal.
In his online writings, Mr. Den Hollander was well aware of Mr. Angelucci’s legal victory and complained that Judge Salas was moving too slowly with his lawsuit.
“The only difference in the Texas case was that two guys were the plaintiffs and a white 70-year-old man was the judge,” Mr. Den Hollander wrote. “Just unbelievable, by now we should have been knocking on the U.S. Supreme Court’s door, but lady unluck stuck us with an Obama appointee.”
Judge Salas, 51, was nominated to the court by President Barack Obama in 2010. She is the first Hispanic woman to serve as a federal judge in New Jersey.
In 2018, she had allowed Mr. Den Hollander’s lawsuit to proceed, a ruling in his favor, but he still ranted about her in his online writings, insulting her and claiming that she was a beneficiary of affirmative action.
Mr. Angelucci was the vice president of the National Coalition for Men, a men’s rights group. About a decade ago, Mr. Den Hollander had approached the coalition and asked its support for his causes and lawsuits, but he was turned away, according to the group’s members.
“We rejected him because we all thought and, it turns out he was, a nut job,” said Al Rava, a lawyer in San Diego who was previously a secretary for the coalition.
Mr. Den Hollander had been a member of the coalition but was kicked out of the group after he made a jarring phone call to Harry Crouch, the coalition’s president, around the time that Mr. Angelucci’s lawsuit was filed.
“He threatened to come to California to kick my ass,” Mr. Crouch said.
When Mr. Angelucci found out about the threat, he called Mr. Den Hollander to chastise him, according to Mr. Crouch.
In his online writings, Mr. Den Hollander criticized the men’s rights movement, suggesting its advocates did not go far enough.
“I don’t belong to that group of wimps and whiners,” he wrote. “They’re trying to win back their rights by acting like girls instead of men.”
Paul Elam, another prominent men’s rights activist, said in a Facebook live video on Monday night that Mr. Den Hollander was “absolutely enraged” about Mr. Angelucci’s pursuit of a lawsuit against the Selective Service Administration, the government agency that maintains a database of Americans eligible for a potential draft.
Mr. Den Hollander viewed the lawsuit as his proprietary domain, believing Mr. Angelucci’s work to be “an intrusion into his space,” Mr. Elam said.
“There was a grudge between the two,” Mr. Elam said.
Mr. Elam did not respond on Wednesday to a request for comment.