Johnny Cash royalties lawsuit launched

The daughters of late country music legend Johnny Cash have launched an investigation into why they never received royalties from his hit, 'Ring of Fire'.

Rosanne Cash and her sisters Kathleen, Cindy and Tara - daughters by Cash's first wife, Vivian - claim not to have received money - estimated to be millions of dollars - from publishing rights to the song, and have hired California lawyer Eric Bjorgum, an intellectual property expert, to investigate the matter.