“And everybody is suspect but you.”

The conversation took place in the autumn of 1975, when Lindenauer, then chief of staff of the Ann Arbor VA Hospital, was grappling with a situation that had thrown the hospital into a panic. As he and co-author Zibby Oneal relate in their new book, Paralyzing Summer, in July and August that year, the number of patients experiencing respiratory failures had spiked dramatically, culminating, on August 15, in three in a twenty-minute period.

The hospital’s chief anesthesiologist, Anne Hill, had been investigating the rash of breathing failures. The only common denominator seemed to be that every patient was receiving intravenous fluids at the time. And by August 15, Hill had realized that the mysterious failures resembled the effects of Pavulon, a powerful muscle relaxant; it’s a synthetic form of curare, a plant-derived toxin famously used by Native South Americans to make poisoned darts.

When she responded to the first attack that day, Hill administered a test for Pavulon–and when it was positive, gave the patient the antidote used to reverse the drug’s effects in surgery. Then, and in each of the two cases that followed, the patients quickly recovered. Convinced there was a poisoner in the hospital, VA staff called the FBI that evening.

Agents headquartered themselves in the hospital for weeks, interviewing every one of the its approximately 750 employees. The investigation eventually identified thirty-five breathing failures over a six-week period as suspected poisonings–ten of them fatal.

Lindenauer was the first person ruled out as a suspect: he was in Europe on sabbatical at the time. Others weren’t working at the time of the attacks or didn’t have access to Pavulon, which was stored in an unlocked refrigerator in the hospital’s intensive care unit, where most of the poisonings took place.

The following summer, a federal grand jury indicted two ICU nurses, Filipina Narciso and Leonora Perez, on ten charges of poisoning, five counts of murder, and one count of conspiracy to commit murder. After a four-month trial and a record thirteen days of deliberation, a jury convicted them of three counts of poisoning and conspiracy. But later that year, judge Philip Pratt granted a defense request for a new trial. By withholding information from the defense and making improper statements in court, he ruled, prosecutors had created “overwhelming prejudice” against the nurses.

A new U.S. attorney decided not to retry them. Released from prison, Narciso and Perez resumed their careers elsewhere; they have never talked publicly about the case.

Now eighty-three and long retired, Lindenauer says he had always planned to write about the poisonings, but it wasn’t until he met Oneal at a dinner party a decade ago that the project was launched.

The author of several acclaimed children’s and young adult books, Oneal enjoyed the challenge. “It was like writing mysteries,” she says. She read trial records, conducted interviews, studied dozens of newspaper articles, and scrutinized the notes Lindenauer took daily while observing the trial.

The book is written in an impersonal, reportorial tone. It respectfully describes the two nurses, both natives of the Philippines who moved to America to better their lives, as well-liked and conscientious caregivers. It makes no definitive statement about their guilt or innocence. But in an interview, Lindenauer admits that reliving the story with Oneal was far from therapeutic: “It brought back to memory how angry I was that someone had assaulted and probably murdered some of my patients, my patients entrusted to my care.” Asked who he thinks did it, he replies with a carefully measured statement: “I agree with the jury.”

He’s well aware that this view may still generate heat. Paralyzing Summer describes an outpouring of sympathy for the nurses in Ann Arbor, including rallies and fundraisers. With memories of anti-Vietnam protests still strong, many residents viewed the FBI with suspicion and found it easy to believe the immigrant women were unfairly targeted. A 1977 Observer article that explained the government’s case, including interviews with four jurors, drew angry reactions from readers.

Greg Stejskal played a small role in the investigation as a rookie FBI agent and wrote about the case in a 2011 article for ticklethewire.com, a website that covers federal law enforcement. He concluded that although “the verdict was set aside, it can not be said the nurses were innocent or that they were ‘falsely accused.'” (The Observer has published several of Stejskal’s reminiscences from his FBI years, including “The Stempel Kidnapping.”) In an interview, Stejskal says that the bureau “would have loved” to have the investigation point to less sympathetic suspects, but “by the time we were done, we felt the facts were overwhelming.”

Along with another former agent, Gene Ward, Stejskal was interviewed for That Strange Summer, a 2015 documentary about the case made by an MSU journalism prof and her students. Narciso and Perez didn’t take part, nor did defense attorneys Tom O’Brien and Ed Stein. But journalists who’d covered the trial, and many supporters who’d rallied to the nurses’ defense, strongly questioned the case against them.

Though critics of the prosecution got most of the screen time, Stejskal considers the film “balanced” and screened it in October as a Rotary Club fundraiser. If more proof were needed that the case remains troubling, the response provided it, as audience members tried to find some other explanation for the deaths. Stejskal answered point by point–but also volunteered his belief that the nurses might never have been convicted if they hadn’t taken the stand themselves. Their testimony contradicted that of other witnesses, undermining their credibility with the jury.

“I know the lawyers [who defended the nurses], and they believed in their innocence,” one person announced. Stejskal replied, “And the prosecutors believed they were guilty.”

Both O’Brien and Stein still practice law in Ann Arbor, “It was a weak and circumstantial case,” says O’Brien, “and the evidence of that is Judge Pratt dropped half the charges” against his clients.

Stein points out the poisonings took place in a “different era.” Security was lax, allowing many people to move freely around the hospital.

So does the defense lawyer think someone else poisoned the patients?

“I don’t know who did it,” Stein replies. But, he adds pointedly, he believes that the FBI doesn’t, either.