William O'Neal, the former FBI informant who infiltrated the Black Panthers in the late 1960s, died after he apparently walked onto a busy expressway and was struck by a car, a newspaper said Thursday.

O'Neal, 40, had been living under the name William Hart since 1973 as part of the Federal Witness Protection Program. O'Neal had lived in California until 1984, when he returned to Chicago.His death Sunday on the Eisenhower Expressway has been ruled a suicide, the Chicago Tribune reported Thursday. But Dr. Robert Kirschner, assistant Cook County medical examiner, said the investigation was continuing.

After running up a criminal record as a car thief on Chicago's West Side, O'Neal was recruited as an FBI informant in 1966 by Agent Roy Martin Mitchell. In exchange for O'Neal's help, Mitchell agreed to forget about a stolen car incident.

After infiltrating the Black Panther Party, O'Neal served as the group's chief of security. He supplied the FBI the floor plan to party headquarters, the target of a controversial 1969 predawn raid in which Panther leaders Fred Hampton and Mark Clark were killed by law enforcement officials.