FBI: Threatening letter sent to Philadelphia judge who is Trump's sister

Authorities are investigating a threatening letter sent to Maryanne Trump Barry, a federal judge in Philadelphia and the sister of GOP presidential front-runner Donald Trump.

The investigation into the letter sent last week to Trump Barry, a senior judge on the Philadelphia-based U.S. Court of Appeals for the Third Circuit, remains ongoing, a spokeswoman for the FBI's Philadelphia office said Monday.

The Secret Service and U.S. Marshals Service are also involved in the probe.

Authorities haven't disclosed where precisely the letter was sent or details about the threat.

A threatening letter was also sent last week to the New York City home of Trump's son, Eric. That letter contained a white powder, though preliminary tests indicated the material wasn't hazardous, the Associated Press reported.