A researcher at the University of Pittsburgh was convicted Friday of first-degree murder after he poisoned his wife last year with cyanide.

Dr. Robert Ferrante now faces a mandatory life sentence for the death of his wife, 41-year-old neurologist Dr. Autumn Klein. Klein was killed in April 2013.

The jury deliberated two days to determine a verdict, but eventually agreed with Allegheny County prosecutors and said Ferrante was guilty of lacing his wife's energy drink with cyanide. He gained access to the lethal chemical by buying it through his lab using a university-issued charge card two days before his wife fell ill.

As the verdict was read, Ferrante hung his head and Klein's relatives in the courtroom burst into tears.

"Justice for Autumn," her mother, Lois Klein, of Towson, Maryland, said outside the courtroom.

The rest of her family issues a statement through the district attorney's office, stating, "While we are pleased that the person responsible for Autumn's death has been brought to justice, nothing will ever fill the emptiness that we feel in our family and in our hearts."

Ferrante, 66, denied poisoning his wife, and his lawyers argued Klein may not have been poisoned at all, bringing in three experts who all claimed that it could not be conclusively proved.

"At a minimum we established very clear reasonable doubt," defense attorney William Difenderfer said when referring to the testimony given from celebrity pathologist Dr. Cyril Wecht. Wecht said he could not be sure about how Klein died due to claims that the test to show cyanide in her blood stream was unreliable.

Ferrante said he bought the cyanide for experiments he was conducting on stem cells for Lou Gehrig's disease, as the toxin kills neurological cells, which simulates what the disease does in the body. However, prosecutors said Ferrante was a "master manipulator," and concocted this plan because he feared his wife was having an affair or going to divorce him.