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In an emotional open letter, Brittany Murphy's mother Sharon Murphy is disputing claims by the actress' father that their daughter was poisoned to death.

"She was my baby, and we stood together throughout Brittany's life. Now I must stand up for her again," Sharon Murphy wrote in a letter to The Hollywood Reporter. "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."

Murphy, who said she has been in seclusion since the death of her daughter four years ago, followed six months later by the death of her son-in-law Simon Monjack, wrote, "Angelo Bertolotti has relocated to California in his old age to claim he is here for Brittany, as he never was in life. He has made outrageous statements over the past few years, culminating in this latest madness: that my darling daughter was murdered."

"His claims are based on the most flimsy of evidence and are more of an insult than an insight into what really happened," Murphy wrote.

Was Brittany Murphy Poisoned to Death?

The Los Angeles Coroner's Office ruled that the 32-year-old actress died in December 2009 of pneumonia, anemia and prescription drug intoxication.

But after legally obtaining samples from his daughter, Bertolotti sent them to a lab for testing. The lab's report showed the presence of heavy metals and suggested that they may have been "administered by a third party perpetrator with likely criminal intent."

"I have a feeling that there was a definite murder situation here," Bertolotti told "Good Morning America." "It's poison, yes, I know that."

Since then, the lab's findings has been questioned by the World Health Organization and two independent toxicologists contacted by ABC News.

Brittany Murphy's Mother-in-Law Wants Probe

Sharon Murphy raised similar questions about the lab results in her open letter and suggested that Bertolotti is trying to gain money and fame with his claims.

"Angelo has shown he only wants to trade on Brittany's life, career and good reputation - even at the cost of putting a cloud over her memory," she wrote.

Meanwhile, the actress' mother-in-law, Linda Monjack, has sided with Bertolotti, telling "Good Morning America," "I do think something is wrong. It doesn't feel right. It doesn't sit right."