A December fire that caused about $300,000 worth of damage to a federal judge’s home in McLean was intentionally set, a Fairfax County fire official said Wednesday.

The blaze does not appear to be related to the official duties of U.S. District Court Judge Liam O’Grady, said Lynzey Donahue, a spokeswoman for the U.S. Marshals.

No one has been charged in connection with the fire and the investigation remains open, said Dan Schmidt, a spokesman for the Fairfax County fire department.

Schmidt declined to say what led investigators to conclude the blaze was intentionally set. Schmidt said the judge’s teenage son was the only one home at the time, but managed to escape without injury after an alarm went off.

The Dec. 5 fire caused extensive damage to the second floor and roof of the home and there was water and smoke damage on the first floor, Schmidt said.

The home was valued at $1.4 million, Schmidt said.

O’Grady was appointed to the U.S. District Court Eastern District of Virginia by President George W. Bush in 2007. He was formerly a U.S. Magistrate Judge in the same district. He also served as a state and federal prosecutor in Virginia.