The 32-year-old died in 2009 and her death was found by the Los Angeles Coroner's Office to be accidental .
It was attributed to multiple-drug intoxication, pneumonia and iron-deficiency anaemia.
But last year, Murphy's father Angelo Bertolotti, sued the Los Angeles Coroner's Office and the Los Angeles Police Department to get further toxicology reports, according to The Hollywood Reporter.
The lawsuit was dismissed, but, according to the Examiner, Bertolotti secured the release of Murphy's hair, blood and tissue for independent testing. He sent the samples to the Carlson Company in Colorado for analysis.
Results supposedly showed the presence of 10 heavy metals above the "high" level set by the World Health Organisation.
Julia Davis, a screenwriter who worked for the US Department of Homeland Security and was working on a biography about Murphy, has also raised the question of poisoning.
"Since the autopsy narrative recorded a number of symptoms synonymous with poisoning, I requested testing for heavy metals/toxins," Davis wrote in an email to The Huffington Post on Monday.
"My suspicions were confirmed.
"Ten heavy metals were found in abnormally high quantities (as much as nine times over the 'high' limit designated by the World Health Organisation).
"These types of heavy metals/toxic elements are commonly found in rat poison, pesticides, insecticides, etc.
"Since neither Brittany nor Simon [Monjack her husband] would have willingly consumed any such substances, the lab concluded that they may have been introduced by a third party with criminal intent."
Davis has now sent requests to law enforcement officials calling for new investigations into Murphy's death.
Five months after her death, Monjack was also found dead, reportedly from pneumonia and anaemia as well.
Bertolotti appears to be trying to clear Murphy's and Monjack's names.
"Vicious rumours, spread by tabloids, unfairly smeared Brittany's reputation," he told the Examiner.
"My daughter was neither anorexic nor a drug junkie, as they repeatedly implied.
"Brittany and Simon were ridiculed by The Hollywood Reporter, when they complained of being under surveillance and in fear for their lives.
"I will not rest until the truth about these tragic events is told. There will be justice for Brittany."
Los Angeles County assistant chief coroner Ed Winter dismissed the findings.
"At the time of their death, both of them were in very poor health," Winter told ABC News, .
"I don't think they ate correctly or took care of themselves. They didn't seek medical attention."
However, Winter admitted the eerily similar deaths were "unusual".
source:1