Rihanna is reportedly cooperating with police in the investigation into the incident on Sunday morning that resulted in boyfriend Chris Brown's arrest for making criminal threats.

More details are emerging about the alleged assault, including reports from TMZ — which had erroneously reported on Monday that Brown was being charged with assault with a deadly weapon in the case — that unnamed law enforcement sources described Rihanna's injuries as "horrific." Photos of the wounds reportedly show major contusions on both sides of the 20-year-old singer's face, with serious swelling and bruising, including a split lip and a bloody nose, as well as bite marks on one of her arms and several fingers.

TMZ also reported that Rihanna initially refused treatment at the scene, but allowed police to take photos of her injuries before being transported to the hospital. The Los Angeles Police Department, citing rules to protect the victims of domestic violence, would not confirm that Rihanna was the victim in the case, but she has been named by a number of media outlets, including the Los Angeles Times, which broke with its editorial policy because of what it described as the high-profile nature of the case, according to HuffingtonPost.com.

Los Angeles police would not confirm to MTV News where the victim was taken for treatment, but Radar Online reported that an unnamed eyewitness saw Rihanna being treated for injuries at Cedars-Sinai Medical Center on Sunday.

"Rihanna was brought through the back entrance on a gurney, flanked by two LAPD officers," the source said. "It was impossible to know it was her at first because when they wheeled her past me, she had the hood on her fuchsia-colored sweatshirt tightly drawn round her face and she was wearing big brown sunglasses. ... I knew the person was famous because of all the attention she was being given by security and medical staff."

The witness said the curtain was not drawn the entire time and they were able to confirm that it was Rihanna and that she was interviewed by police for nearly an hour. "Rihanna was clearly very upset by what had happened and I could hear her screaming," the eyewitness said. "Rihanna was trying to get her point across about something; she sounded like she was crying as she tried to get to put her point across."

Brown reportedly fled the scene of the incident on foot with the keys to the rented silver Lamborghini the couple was driving in following the alleged attack, leaving Rihanna "beaten really badly and hysterical" by the side of the road, a source told E! Online.

"Rihanna didn't want anyone to touch her, she was in so much pain," the source said. A member of the 20-year-old's "inner circle" told E! that Rihanna's family is making plans to get her out of Los Angeles. "They want to get her back to Barbados. They want to keep her away from Chris right now."

Brown and Rihanna, who had been dating for a year, had reportedly hit a rough patch recently. They attended Clive Davis' annual pre-Grammy party on Saturday night prior to the alleged incident, but, according to reports, got into a heated argument in the car ride home following the event.

Spokespeople for the artists have made no public statements in the wake of the scandal.

Brown was booked on felony criminal threats on Sunday and released on $50,000 bail. He could reportedly face additional domestic-violence counts should the district attorney decide to press charges; the D.A.'s office has not yet received the case for review. He is scheduled to appear in court on March 5.

Get resources and information about domestic violence, or check out Think MTV for a video handbook on spotting the warning signs of abuse.

[This story was originally published on 02.10.09 at 9:38 a.m. ET]