Catherine Margaret Birnie was born Catherine Harrison in Perth on May 31, 1951. Her mother died when she was a small child and she was raised by grandparents in circumstances she described as loveless. She met David Birnie as a teenager and the two committed burglaries together; she served time for it. She then married another man, had six children, and by all accounts was a competent mother for a decade.
In 1985 she left that family and went back to David Birnie, and the change in her was total. Over five weeks in October and November 1986 the two of them took Mary Neilson, Susannah Candy, Noelene Patterson and Denise Brown, held them chained in the spare room of the house in Willagee, and killed them. Catherine's part was direct: she helped restrain the women, was present throughout, and by her own admission was jealous of Noelene Patterson, whom David wanted to keep alive, and pressed him to kill her.
On November 10 she loosened the chain on a seventeen-year-old captive and went to answer the telephone. The woman went through the window and got to a shopping centre in Fremantle. It is not established whether that was carelessness or something else, and Catherine Birnie has never said.
She pleaded guilty in February 1987 to four murders and was given four life sentences with a recommendation of never to be released. She is held at Bandyup Women's Prison in Perth and has never applied for parole. The Western Australian attorney general confirmed in 2007 that she will die in custody.