Updated

Someone taped a profane, derogatory note to the window of a restaurant where a federal judge whose mother and husband were killed earlier this year was dining under the protection of U.S. Marshals, authorities said.

The note, placed on the window Friday night, did not specifically name U.S. District Judge Joan Humphrey Lefkow (search), but authorities believe it was likely intended for her, said John O'Malley, assistant chief deputy for the Marshals Service in Chicago.

"We're taking it seriously and trying to get to the bottom of who left it," O'Malley said. He declined to comment further, saying it could compromise the judge's protection.

Witnesses said they saw a man tape the note to the window of Amarit Thai Restaurant (search) before disappearing into the crowd on the street, according to police. U.S. Marshals were on duty inside and outside the building, police said.

Lefkow has been under federal protection since the February slayings of her husband and mother in the couple's Chicago (search) home.

In March, Bart Ross, a 57-year-old unemployed electrician from Chicago, committed suicide in suburban Milwaukee after leaving a note confessing to the murders. DNA evidence later connected Ross to the crime scene. He had been angered when Lefkow dismissed a malpractice suit he had filed, authorities said.

The judge also once was the subject of a murder plot by white supremacist Matthew Hale, according to prosecutors. A federal jury convicted Hale in April 2004 of soliciting her murder. She was never attacked.

Hale was sentenced last month to 40 years in prison.