"This is what's killing all of us. How did it happen? Her mum, myself and her family—we want to know why we lost our baby," Simon Monjack tells People.
And, while he confirms that doctors at the hospital told him she died of cardiac arrest, all he can do is eliminated possible origins of that heart failure.
A drug overdose, he insists, is out of the question.
"I can get rid of that [rumor] right now," he says.
According to him, eating disorders weren't the cause, either.
"These rumors that she was anorexic? It's crazy—she was slim, but that was her natural physique," he claims, later adding, "She tried to gain weight but had one of those metabolisms—a high metabolism—but enjoyed food as much as anyone."
Monjack goes on to explain why he was initially opposed to an autopsy.
"My initial reaction to the autopsy was—they're going to cut her open—I couldn't bear it. That would break her mother," the screenwriter tells the magazine. "But we realized we needed to know. I look forward to getting the results."
The findings of the autopsy, which happened yesterday, won't be available for up to six weeks, pending the toxicology report.
The evening before her death, Murphy was feeling under the weather, resting all day in her "monkey pajamas" and treating laryngitis with herbal tea, ginger and lemon. Monjack also explained that the actress had a heart murmur, which can result in dizziness, fatigue and irregular heartbeats, but isn't typically life-threatening.
"She was on herbal remedies that wouldn't speed up her heart," he says. "There was nothing here that could endanger her; there was prescription medication in the house for her female time and some cough syrup. That was it."
The pair was planning to start a family in 2010. Monjack says having a baby was his wife's "big dream," and describes himself as lucky.
"We are faced with the ridiculous reality that people out there believe she felt, 'Oh, poor me, I'm fat, I'm think.' Brittany didn't see beauty as a physical thing, which I'm bloody lucky for," he laughs. "I know there was a disparity in how we looked and I'm no movie star, but she always saw the person."