PITTSBURGH — A medical researcher charged with poisoning his wife had a computer on which someone conducted searches relating to cyanide poisoning two or three days after she died, a state police computer expert testified Tuesday.

The searches found on 66-year-old Dr. Robert Ferrante’s laptop occurred days before test results on Dr. Autumn Klein’s blood revealed a fatal level of cyanide and as doctors remained baffled by her death.

Earlier in the fourth day of what’s expected to be a three-week trial, one of Ferrante’s lab assistants testified he placed an overnight order for potassium cyanide two days before Klein fell ill in the couple’s kitchen. Another lab assistant said he was acting a “little bizarre” around the time his wife fell ill.

In the days after her death, Ferrante had told friends and family he believed she died of a sudden, unexplained illness such as a stroke. Despite that, computer expert Cpl. John Roche testified one of the searches typed into Yahoo Answers on his computer was: “How would a coroner detect when someone is killed by cyanide?”

Under cross-examination, Roche acknowledged he can’t prove whether Ferrante or someone else did the computer searches.

Some of the searches were done as early as January 2013, including one seeking the legal definition of “malice of forethought” — an apparent reference to malice aforethought, a legal term that means premeditation.

Investigators contend Ferrante, an expert on Lou Gehrig’s disease, laced Klein’s creatine energy drink with the poison on April 17, 2013, after telling her in text messages that it would help them conceive another child. The couple already had a 6-year-old daughter, but Klein was said to want another because she didn’t want the girl to be an only child. Klein, 41, fell suddenly ill that night and was dead three days later.

Ferrante disputes his wife was poisoned and denies any involvement in her death.

Amanda Mihalik, now a medical student at the University of Florida, had worked in Ferrante’s University of Pittsburgh lab and testified he “seemed a little bit different that week” and “a little bizarre.” Among other things, she saw him mixing substances in a laboratory beaker and drinking them at a sink, a violation of lab policy.

Another lab assistant had previously testified that Ferrante’s overnight order using a university credit card was the first time in six years that cyanide had been seen in the lab.