LOS ANGELES – Robert Plant and Alison Krauss’ unorthodox partnership yielded rich rewards on Grammy night, as the pair nabbed five awards for their haunting “Raising Sand,” including record and album of the year honors. But their sweep was overshadowed before the show even began when police announced that Chris Brown, himself a double nominee and scheduled performer, was being investigated for allegedly assaulting an unidentified woman the night before. Brown turned himself in to authorities and was briefly held before posting $50,000 bail Sunday night, jail records showed.

Brown and longtime girlfriend Rihanna, also nominated, were both slated to perform in different slots of the show, but separately dropped out at the last minute. The victim of Brown’s alleged assault wasn’t identified, and it wasn’t immediately clear whether Rihanna’s absence was related to Brown’s.