The murder trial of Marybeth Tinning opened in Schenectady County Court on June, 22, 1987. The prosecuting attorney, John Poersch, had been on the case since before Marybeth was arrested. During contentious pre-trial hearings, the prosecution argued successfully that the crucial statements made by the defendant on February 4, 1986 at State Police headquarters were not coerced and would be admissible. Marybeth's full 36-page confession would be available at trial. "Once you have heard all of the evidence and assimilated it," Poersch said in his opening statement, "you will come back with a verdict of murder in the second degree against Marybeth Tinning, who murdered her child by smothering it." Defense attorney Paul Callahan challenged the prosecution to come up with a cause of death for Tami Lynne. "That is going to be very critical," he said to the jury, "How did this child die?" (June 23, 1987, Knickerbocker News).
The medical testimony at the trial was complex, involving several doctors, all experts, who held different opinions on the disturbing tendencies of the Tinning children to die suddenly and without explanation. Some of the testimony helped the defendant. Other portions were extremely damaging. Dr. Bradley Ford, who examined Tami Lynne when she was an infant, advised the Tinnings that in view of their family history, a crib monitor should be installed. The device would sound an alarm if Tami Lynne stopped breathing. Curiously, Marybeth refused. "The monitor was recommended," he told the court, "but the parents elected not to use it" (June 25, 1987, Knickerbocker News). Ironically, the doctor did not insist on the monitor because the baby was in such good health. Dr. Thomas Oram testified on the cause of death. He denied that Tami Lynne died from SIDS. "I'm saying sir, in essence that I came to the definite, positive conclusion that this child was smothered," said Dr. Oram to the court, "This would be the only thing that would answer all the evidence" (July 1, 1987, Knickerbocker News).
The defense called several physicians to the stand to refute that allegation and to offer evidence that all the Tinning children suffered from a genetic defect. Dr. Arnulf Koeppen, a pathologist at Albany Veteran's Administration Hospital, told the court that it was his belief that Jonathan, the seventh child, had died from Wernig-Hoffman Disease, a genetic disease that attacks the spinal column. When pressed on that assertion, he was unable to state that Tami Lynne had that disease as well. Dr. Jack N.P. Davies, a well-known pathologist, went a step further. He claimed that the affliction that killed all nine children was unknown. "Frankly," he said to the court, "I think this may be a new syndrome, a new disease" (July 6, 1987, Knickerbocker News).
However to refute defense claims of genetic diseases, the prosecution called Dr. Marie Valdez-Dapena, a nationally recognized expert on Sudden Infant Death Syndrome. Noting that Tami Lynne had a perfectly normal spinal column, she said that "it's highly unlikely that this is a case of Werdnig-Hoffman Disease." Rather, she believed that "there is a stronger probability that this was a suffocation with a soft object, in light of the family's history" (July 8, 1987, Knickerbocker News). Following Dr. Valdez-Dapena's testimony, the defense was allowed to call further witnesses to refute the prosecution's medical experts. It became the battle of the doctors with both sides calling six pathologists, all who had different opinions on how Tami Lynne died. Dr. John L. Emerey had the most interesting observation. "I'd like to investigate the family," he said, "The ideal experiment would be to let her have more children and look at them biochemically" (July 10, 1987, Knickerbocker News).
In closing statements, District Attorney Poersch stood on the facts of the case and relied on the jury's common sense. "I don't think there is any question that the prosecution has proved this case," he told the court, "I don't think there is any other thing we could offer to substantiate that Mary Beth Tinning killed those three children" (July 16, 1987, Albany Times Union). Defense counsel Paul Callahan appealed to the jury's sense of fair play. "Don't be led into the conclusion that there are inferences and innuendos that are proof that she may have killed Tami Lynne," he told the jury in his summation. "If she didn't cry at the right time, if she laughed at the wrong time, does that mean she is guilty of murder," he added, "or that she's a human being with emotions?" (ibid)But the jury could not help noticing one important point. Marybeth Tinning, who was accused of the worst crime a mother could commit, who had been labeled a baby killer and faced a life sentence in prison if convicted, had refused to take the witness stand in her own defense.