A gunman opened fire at the home of US District Court of New Jersey Esther Salas on Sunday in North Brunswick, killing her son and injuring her husband, according to the federal courthouse’s top judge.

Daniel Anderl, a 20-year-old student at Catholic University, has died, and Mark Anderl, the judge’s husband and a defense attorney, was injured, according to Chief Judge Freda Wolfson. Salas was unharmed, Wolfson said.

Both the US Marshals and FBI are investigating the shooting and working to find the suspected gunman. Initial reports from law enforcement said Daniel Anderl opened the door with his father right behind him. The door opened to a hail of gunfire and the gunman fled, a law enforcement source told CNN.

“We are looking for one subject,” the FBI said in a statement. “We are working closely with our state and local partners and will provide additional updates when available.”

The gunman appeared to be wearing a FedEx uniform, a law enforcement official with direct knowledge of the investigation told CNN.

It is not yet known whether the gunman was a FedEx employee or someone posing to be an employee.

“We are aware of the media reports and are fully cooperating with investigating authorities,” Jonathan Lyons, a spokesman for FedEx, said in an email statement.

Law enforcement has not been aware of any threats against the judge, the source told CNN. Right now investigators don’t know the motive.