The FBI is investigating whether a self-described “anti-feminist” lawyer, suspected of killing the son of a federal judge, had previously murdered a fellow lawyer in California. Roy Den Hollander, an attorney known for bringing lawsuits over perceived infringements of men’s rights, was found dead in the Catskills area of New York on Monday, a day after Daniel Anderl, the 20-year-old son of US district judge Esther Salas was shot and killed in New Jersey. Federal agents are now exploring whether Den Hollander had any role in the killing of Marc Angelucci, a men’s rights lawyer who was shot dead in southern California earlier this month, according to Associated Press. Den Hollander is the prime suspect in the murder of Anderl. Officials say a man posed as a delivery driver at Salas’s home, before killing Anderl and shooting and wounding Salas’s husband, Mark Anderl. The shooting bore similarities to Angelucci’s murder, an FBI official told the Associated Press. In both incidents the suspect posed as a FedEx driver before opening fire. Angelucci, 52, was killed at his home in San Bernardino county on 11 July. Investigators are examining Den Hollander’s financial and travel records, as well as misogynistic missives he posted online, the official said, to determine whether he was responsible for shooting Angelucci. The California lawyer was the vice-president of the National Coalition for Men, an organization which “raises awareness about the ways sex discrimination affects men and boys”, according to its website. Salas was at home in New Jersey at the time of the shooting on Sunday, but was unharmed. The judge was nominated to the federal court by Barack Obama, and confirmed in 2011. In 2015 she was the judge in a lawsuit filed by Den Hollander, which alleged a male-only military draft discriminated against both men and women. In more than 2,000 pages of often misogynistic, racist writings, Den Hollander had criticized Salas’s life story of being abandoned by her father and raised by her poor mother as “the usual effort to blame a man and turn someone into super girl”. Den Hollander filed multiple lawsuits challenging what he saw as unfair treatment of men. He had brought a series of unsuccessful lawsuits challenging the constitutionality of “ladies’ night” promotions at bars and nightclubs. The eye-catching litigation, and Den Hollander’s willingness to appear on television, had earned him spots on The Colbert Report and MSNBC. Den Hollander’s body, along with a package addressed to Salas, was found in Sullivan county, New York, after he reportedly shot himself.