PITTSBURGH — Jurors who convicted a University of Pittsburgh researcher of first-degree murder in the cyanide poisoning death of his wife say they didn’t find his explanations believable and were moved by a 911 call.

Dr. Robert Ferrante, who hung his head when the verdict was read in court Friday, faces a mandatory life sentence in the April 2013 death of his wife, 41-year-old neurologist Dr. Autumn Klein.

“I think he had incredible coaches,” juror Helen Ewing said. “I think he had a year to think about what story he wanted to tell.”

Ewing said she was “horrified” by the suffering of Klein heard on the 911 call Ferrante made while his wife was groaning, moaning and gasping for air in the background.

The jury, which deliberated for 15 hours over two days, agreed with Allegheny County prosecutors who accused Ferrante of lacing his wife’s creatine energy drink with cyanide he bought through his lab using a university-issued charge card two days before she fell suddenly ill.

Klein’s relatives burst into tears upon hearing the guilty verdict.

The Klein family issued a statement through the district attorney’s office, saying, in part, “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.”

The 66-year-old Ferrante denied poisoning his wife. His lawyers made the case that she might not have been poisoned at all, citing three defense experts who said that couldn’t be conclusively proved.

“At a minimum we established very clear reasonable doubt,” defense attorney William Difenderfer saide.

Ferrante will be formally sentenced Feb. 4.