PITTSBURGH — A University of Pittsburgh medical researcher is either guilty of intentionally poisoning his wife or is “the unluckiest man in the world,” a prosecutor said Thursday.

Assistant District Attorney Lisa Pellegrini made that comment in her closing argument in the first-degree murder trial of 66-year-old Dr. Robert Ferrante.

Ferrante has denied lacing his 41-year-old wife’s energy drink with cyanide last year, saying he bought the poison for his research on stem cells as he sought a cure for Lou Gehrig’s disease.

His attorney told the jurors in his closing argument that defense experts expressed doubts about whether Dr. Autumn Klein was murdered at all, which should lead to acquittal.

Ferrante took the stand Wednesday and acknowledged doing online searches on cyanide poisoning and related subjects in the weeks and months before his wife died. But Ferrante testified the searches were related to his research.