11/25/2013 at 02:10 PM EST
's mother Sharon has come forward to dispute claims by Brittany's father that her daughter may have been intentionally poisoned before her death in 2009
"I have chosen to stay out of the limelight since the tragic and sudden death
of my wonderful, talented, loving daughter four years ago this Dec. 20," Sharon Murphy writes for The Hollywood Reporter
in response to an assertion by Brittany's estranged father, Angelo Bertolotti, that a new lab test reveals the possibility of foul play.
"I have no choice now but to come forward in the face of inexcusable efforts to smear my daughter's memory by a man who may be her biological father, but was never a real father to her in her lifetime," Sharon writes. "He has made outrageous statements over the past few years, culminating in this latest madness: that my darling daughter was murdered."
Sharon says that Bertolotti did not parent Brittany as she was growing up, only to resurface when Brittany's acting career started going well.
"Angelo did come out of the woodwork when Brittany was a teenager and found success in a number of TV shows just before she was in Clueless
, she says. "But she quickly saw him for who he is – and didn't want anything to do with him."
Bertolotti alleges the Los Angeles County Coroner should have investigated further and done more testing before determining that both his daughter and his son-in-law, Simon Monjack
, died young and only five months apart from natural causes. He sued the coroner last year, and recently held up a lab report, based on Brittany's hair samples, as proof of possible poisoning.
"My theory is that the mother did the job on both of them," Bertolotti tells PEOPLE. When asked what motive Sharon Murphy might have had, he said, "Money, that's all I can understand about it." He added he had no idea how much money, if any, Sharon may have collected from insurance or her daughter's estate.
The testing, by the Carlson Co. out of Colorado Springs, Colo., found high levels of 10 heavy metals. "If we were to eliminate the possibility of a simultaneous accidental heavy metals exposure to the sample donor then the only logical explanation would be an exposure to these metals (toxins) administered by a third party perpetrator with likely criminal intent," the lab wrote.
Forensic experts consulted by PEOPLE and other media organizations say the report does not prove foul play, and there are many possible innocent explanations for the heavy metal findings, such as hair dye.
"Many of these trace metals are found in food additives, laxatives and other types of materials someone like the deceased in this case would be taking for (various) reasons like keeping in shape etc.," Dr. Bennet Omalu, a pathology professor at UC Davis, tells PEOPLE. "You cannot determine this case to be a homicide solely based on the prevailing toxicologic profile. "
Sharon argues that Bertolotti's lab is merely an "Internet site" that created a false report, and although she initially disputed the possibility of toxic mold
as a cause in her daughter and Simon Monjack
's deaths, she now concedes that it may have been a factor.
"We will never know for sure," Sharon says. "However, we do know the Los Angeles County Coroner did extensive tests and found that she died of natural causes. And now she is a real living angel in heaven."
Julia Davis, a spokeswoman for Bertolotti, insists Bertolotti did have a good relationship with his daughter, and that it is Sharon, not Bertolotti, who has profited off their daughter.
"Why would an old man at the end of his life be trying to profit off of his daughter?" Davis said, adding, "the lab is accredited, and we question why Sharon would not want to know what really happened."
When asked if Mr. Bertolotti stands by his statement that he believes Sharon is responsible for their daughter's death, Davis said, "The anger of the ex-spouses is not something we want to concentrate on … obviously they hate each other greatly."
An official at Carlson had no comment on the case.