02/11/2009 at 04:45 PM EST
Police are continuing to gather evidence in their case against R&B singer Chris Brown
after prosecutors requested more details from detectives on Tuesday.
"It's our understanding the LAPD won't return the case to us this week," said L.A. District Attorney spokeswoman Jane Robison. "Once we get it, we will review it again to determine if there's a case."
LAPD officials had no comment.
Brown, 19, was booked on a felony criminal threat
charge on Sunday after allegedly attacking
, 20, earlier that day.
A legal expert says that DAs frequently ask police to further investigate cases before they file formal charges.
"The DAs probably kicked it back to police simply because they needed more evidence, such as medical records, or perhaps they wanted Rihanna re-interviewed to make sure her story hasn't changed," says L.A. defense attorney Steve Sitkoff, who's not involved with the case.
"This doesn't imply the detectives did sloppy work," Sitkoff adds. "The fact that this case is high profile cuts two ways. On one hand, DAs want to show the public the case is handled expeditiously. And on the other hand, they don't want to make hasty decisions."
Despite a police source confirming multiple injuries to Rihanna's face, Sitkoff says Brown could be charged with anything from misdemeanor battery on up to several felonies – or nothing at all.
"There's just too many variables to make a guess at this point," he said.