LOS ANGELES, May 25 (UPI) -- The FBI has launched an investigation into the fatal shooting of a homeless black woman by a Los Angeles police officer. The move came one day after civil rights activists demanded an investigation into the shooting of the woman, identified as Margaret Laverne Mitchell. Assistant U.S. Attorney Michael J. Gennaco says he asked for the federal probe to determine whether the officer used excessive force or violated the civil rights of the 54-year-old woman, who was a college- educated bank employee until she was forced onto the streets by mental illness. Police say the woman pushed her shopping cart into the officers and tried to stab one of the officers with a large screwdriver after they stopped to question her last week about a number of shopping cart thefts in the area. Police say 27-year-old Officer Edward Larrigan had to move suddenly to avoid being stabbed and fired one shot as the woman continued to try to attack him. She was shot in the upper torso and died soon afterward at a hospital.  