Medical examiners performing an autopsy on Bobbi Kristina Brown said Monday their initial findings turned up no obvious cause of death, while experts said the months that have passed since Brown was found face-down in a bathtub are working against authorities now tasked with solving how she died.

The Fulton County Medical Examiner’s Office said in a statement Monday afternoon that it will likely be several weeks before it can rule on a manner and cause of death for the 22-year-old daughter of Whitney Houston. The agency said its initial autopsy turned up “no significant injuries” or “previously unknown medical conditions.” It said the next step is ordering lab tests and issuing subpoenas for documents — most likely Brown’s hospital records.

Experts said time is definitely an enemy in Brown’s case. Any drugs she might have taken passed from her bloodstream long ago. Physical injuries would have been healing even as Brown remained largely unresponsive. If police overlooked any physical evidence at Brown’s home after she was hospitalized Jan. 31, recovering it nearly six months later may be impossible.

Dr. Michael Baden, former medical examiner for New York City, has performed more than 20,000 autopsies during a career spanning more than 45 years. He said the first obstacle for forensic pathologists in Brown’s case will be a living body’s ability to mend itself and erase medical evidence.

“Normally, when we do autopsies, we do them in people who freshly died. Things like toxicology and injuries are clear,” said Baden, who helped investigate high-profile cases including the deaths of comedian John Belushi and civil rights worker Medgar Evers. “Because she was in the hospital for a long time, any drugs that may have been in the body will be gone after a few days. Injuries, if there were any injuries, would be changed by the length of time, the healing process.”

That means Brown’s hospital records will be as important, if not more so, to medical examiners investigating her death as physical evidence from her autopsy.

Baden said it’s highly possible doctors screened Brown’s blood for drugs as soon as she was admitted to the hospital. Her medical charts may also note any physical injuries observed by doctors who first treated her. The initial report by emergency medical technicians who first responded to Brown’s home could also yield critical clues, he said.

Dr. Henry Lee, the forensic scientist whose famous cases include the death of child beauty queen JonBenet Ramsey, said the passage of time could make Brown’s autopsy “much harder.”

But he said valuable clues could possibly still be gained from examining her lungs and digestive system. And lab tests of any clothing she may have worn the day she was rushed to the hospital could turn up residue of drugs or other toxins.

“There’s a lot of stuff you can do,” Lee said.

The Roswell Police Department in suburban Atlanta is still investigating the events that led to Brown’s death, authorities say. A police report described what happened in the townhome Brown shared with Nick Gordon as a drowning. However, no one has been charged in the case.

Gordon has said Bobbi Kristina, whose father was R&B singer Bobby Brown, wasn’t breathing when she was found face-down in the tub — and that she lacked a pulse before first responders arrived. The scene was similar to how Houston was found dead in 2012 in what authorities later ruled an accidental drowning.

In the case of solving her daughter’s death, much will depend on how thorough an investigation police launched when Brown was first hospitalized in January, said Ken Hodges, a former Georgia prosecutor who’s now a defense attorney in Atlanta.

“The level of intensity that law enforcement gives things oftentimes is based on the severity of what they’ve got,” said Hodges, who served 12 years as district attorney in Dougherty County. “In a homicide, it’s often given to the more seasoned detectives. If this is perceived at the beginning as a drug overdose and not necessarily criminal, it may not be investigated at all or might be given to a less experience detective.”

Any fingerprints, blood, hair samples or other physical evidence that police failed to collect six months ago would likely now have vanished, Hodges said. Or any evidence still at the scene months later — such as a fingerprint on a doorknob — would have far less value now because of potential comings and goings since.

Likewise, Hodges said, any witnesses who weren’t interviewed by police at the time might have trouble remembering events correctly.

“They may have done it all six months ago,” Hodges said. “But time is never a law enforcement officer’s or a prosecutor’s friend. It’s always best to jump on a case early. Evidence disappears; memories fade. Things happen.”

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Bynum reported from Savannah, Georgia.