Authorities continue to investigate what went wrong early Sunday morning in Brown's rented Lamborghini in Los Angeles' ritzy Hancock Park neighborhood just minutes after Brown and girlfriend Rihanna left a pre-Grammy party.
Officers received a 911 call about an incident in which a woman accused Brown of hurting her, L.A. Police Sgt. Bridget Pickett said. Authorities did not identify the caller, citing confidentiality for victims of domestic abuse, but insiders told Fox 411 that it was Rihanna.
Her vehicle was later spotted at Cedars-Sinai Hospital in Los Angeles, and an eyewitness told Radaronline.com that Rihanna, 20, had been seen at the hospital.
TMZ.com has also confirmed that Rihanna, whose real name is Robyn Fenty, was the alleged victim in the case, and quotes a law enforcement source who said she suffered "contusions and bite marks."
Brown, 19, who left the scene before authorities arrived, turned himself in to police while the Grammy Awards were going on Sunday night without him and Rihanna.
Brown was released after posting $50,000 bail. Pickett described the singer as "professional" during processing.
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Brown was booked for making criminal threats, rather than for domestic abuse, since the victim had “visible injuries.” A criminal threats conviction can carry up to nine years in prison. A domestic abuse conviction carries up to four years.
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Brown's representatives refused to discuss any of the allegations, or his arrest. Rihanna's publicist declined to say why the singer did not appear, saying only that she was "well" and expressing thanks for the concern. A phone message left with Brown's attorney Geragos was not immediately returned.
News of the incident broke as stars were showing up at the Grammys. Police said in an initial news release, sent 90 minutes before the show began, that the woman accusing Brown showed visible injuries.
Less than an hour after the ceremony ended, Brown left a police substation with his attorney.
Pickett said Brown did not appear to have any physical injuries, and she did not know who placed the 911 call. A police spokeswoman said the department would not release the tape.
Brown's $2,000-per-day rented Lamborghini appeared to have been impounded at a police lot following the incident, TMZ.com reported.
Brown did not win in either category for which he was nominated: pop collaboration with vocals for No Air and male R&B vocal performance for Take You Down.
The Associated Press contributed to this report.