The LAPD's preliminary investigation into the death of Brittany Murphy has established that there is no evidence of foul play or other criminal activity, sources say.

Police are now waiting for the Brittany Murphy autopsy results from the L.A. County Coroner. If the results raise red flags, the LAPD may pursue the matter further.

Investigators believe, pending the autopsy, that Murphy died of natural causes. But autopsy results have been deferred pending toxicology and neurological tests.

Still, the LAPD has not formally closed the investigation because of the possibility that Murphy, who passed away Sunday, overdosed on prescription medication.

“We are keeping the investigation open until the toxicology reports are available in five to six weeks,” an LAPD source privy to the investigation told Radar Online.

The late Brittany Murphy (1977-2009).

Given how much medication was found in her house, a source says “We are focusing on possible overdose scenarios including looking at prescription medicines.”

Coroner's office officials took a sample of her brain for testing. It will take weeks for test results to come through, along with various toxicology screenings.

Early yesterday, the 32-year-old actress was transported to Cedars Sinai Medical Center in L.A. after falling ill and being found unconscious in the bathroom.

Three attempts to resuscitate her failed and she was declared dead after suffering from cardiac arrest. She is survived by her husband, Simon Monjack.

More information to follow as the story develops ...