PITTSBURGH — A University of Pittsburgh medical researcher who had said through his attorneys he was “devastated” by his neurologist wife’s sudden death last year took the witness stand to deny killing her with cyanide.

Allegheny County prosecutors contend Dr. Robert Ferrante, 66, a leading researcher into Lou Gehrig’s disease, laced his wife’s energy drink with the poison on April 17, 2013. She fell suddenly ill that night and died three days later.

Closing arguments were scheduled today before the jury must deliberate whether Ferrante is guilty of first-degree murder in the death of 41-year-old Dr. Autumn Klein. If convicted, Ferrante faces a mandatory life sentence.

Ferrante and his defense attorneys contend they believe Klein may have been stricken by a cardiac arrhythmia or some kind of brain abnormality relating to headaches and fainting spells she had suffered in the previous months. They’ve attempted to cast doubt on a lab test that found a fatal level of the poison in her blood by noting other blood tests either weren’t completed, or found cyanide metabolites at non-lethal levels, which is common in humans.

Assistant District Attorney Lisa Pellegrini told the jury in her opening statement that Ferrante bought the poison using a university charge card. Ferrante has said the toxin was useful in replicating the kind of cellular death he studied in his laboratory.

Defense attorney William Difenderfer asked Ferrante if the cyanide “was purchased for the purpose of you plotting or planning to kill your wife?”

“Absolutely not,” Ferrante said.

“Would you, on the 17th of April, or anytime, would you have ever harmed your wife?” Difenderfer followed up.

“No,” Ferrante said.

Pellegrini used Ferrante’s description of the night his wife fell ill in an effort to undermine his credibility.