(CNN) - The son of United States District Court judge for New Jersey, Esther Salas, died after a gunman opened fire at his North Brunswick home on Sunday, the highest judge of the federal court confirmed to CNN .
Judge Freda Wolfson told CNN Sunday night that Salas' son Daniel Anderl, 20, was killed in the shooting and her husband, Mark Anderl, was wounded. Salas was unharmed, Wolfson said.
Both the US Marshals and the FBI are investigating the shooting. Initial police reports said Daniel Anderl opened the door with his father right behind him. As the door opened, a hail of gunfire came and the gunman fled, a police source told CNN.
"We are looking for a subject," the FBI said in a statement. "We are working closely with our state and local partners and will provide additional updates as they become available."
The gunman appeared to be wearing a FedEx uniform, an agent with direct knowledge of the investigation told CNN.
It is not yet known if the gunman was a FedEx employee or someone who posed as one.
"We are aware of the media reports and we are fully cooperating with investigative authorities," Jonathan Lyons, a FedEx spokesman, said in an emailed statement.
Police were unaware of any threats against the judge, the source told CNN. Investigators at this time do not know the reason for the shooting.
"Judge Salas and her family are in our thoughts right now as they face this senseless act," New Jersey Governor Phil Murphy said in a statement. "This tragedy is our last reminder that armed violence continues to be a crisis in our country and that our work to make every community safer is not being done."
US Democratic Senator Bob Menéndez, who said he was proud to have recommended former President Barack Obama to Judge Salas, also released a statement dedicating his prayers to the family.
"My prayers are with Judge Salas and her family, and that those responsible for this horrendous act are quickly arrested and brought to justice," said Menéndez.
North Brunswick Mayor Francis "Mac" Womack told CNN by phone Sunday night that Judge Salas' husband, Mark Anderl, is "one of the most honest lawyers" he has dealt with.
"He is a very exuberant, vibrant, and one hundred percent personable person," said Womack. "He loves to talk about his wife and he loves to brag about his son, and how his son stood out in baseball and how he was doing in college in Washington ... I'm so sorry he's going through this."
The FBI urged anyone with relevant information to call the FBI Newark at 973-792-3001.
CNN's Mitchell McCluskey, Ganesh Setty and Sonia Moghe contributed to this report.