An anti-feminist lawyer found dead Monday is suspected of killing the son of a US federal judge and wounding her husband at their New Jersey home, investigators said.

The FBI has identified Roy Den Hollander as the main suspect in the shooting attack on Judge Esther Salas's family on Sunday, US prosecutors said in a statement.

Hollander's body was found in New York state on Monday morning, hours after the shooting. He had apparently shot himself, US media reported citing law enforcement officials.

Judge Esther Salas was not hurt in Sunday's attack, ABC News said.

Her son Daniel Anderl, 20, was shot dead when he answered the door, ABC and CNN said, citing sources.

"He was shot through the heart," North Brunswick mayor Francis Womack, a friend of the judge, told ABC.

The judge's husband Mark Anderl, a criminal defense attorney and former prosecutor, was in critical but stable condition after undergoing surgery, the New Jersey Globe reported.

The gunman appeared to be dressed as a FedEx driver, according to reports citing law enforcement sources.

The office of the US attorney for New Jersey did not offer a motive for the crime and said its investigation was ongoing.

The FBI said they were looking for one suspect in the shooting
Representational image AFP / Johannes EISELE

Den Hollander was a self-described anti-feminist lawyer who filed numerous lawsuits targeting women in recent years, US media reported.

He had sued nightclubs for offering ladies' night discounts and Columbia University for offering courses on women's studies, said The New York Times.

In 2015, he brought a lawsuit before Salas that challenged the men-only military draft, said US media.

On his website, he called on men "to fight for their rights before they no longer have them."

Judge Salas, 51, was the first Hispanic woman to serve as a federal district judge in New Jersey and was nominated to her current position by President Barack Obama in 2010.

"I know Judge Salas and her husband well, and was proud to recommend her to President Obama for nomination to New Jersey's federal bench," New Jersey Senator Bob Menendez said in a statement quoted by media.

"My prayers are with Judge Salas and her family, and that those responsible for this horrendous act are swiftly apprehended and brought to justice."

The judge is currently assigned to a class-action lawsuit filed by a group of Deutsche Bank investors who say the bank failed to properly monitor customers it had deemed to be high-risk -- including convicted sex offender Jeffrey Epstein, who killed himself last year while in prison awaiting trial.

Salas has handled several high-profile cases and presided over the 2014 fraud trial of "Real Housewives of New Jersey" star Teresa Giudice and her husband Joe.