Singer Billy Joel hired Sir Paul McCartney's private investigator to track down a woman charged with stalking his daughter. Alexa Ray Joel allegedly received over 60 threatening Facebook.com messages from Sheryl Finley over the past few months, prompting her Piano Man father to call on chiefs at a European security firm, who previously worked for his pal McCartney, to launch an investigation into the case. A source tells the New York Post, "Her mother, Christie Brinkley, was terrified that someone would harm her baby. Billy Joel was worried but focused." Detectives ultimately found 40-year-old Finley, who spent time in a mental institution in 2010, in Austin, Minnesota and she has since been charged with felony and gross misdemeanour stalking for repeatedly sending electronic messages.