A letter purporting to be from a juror who was bribed to rule for the University of Iowa in a major medical malpractice case was likely a hoax by someone upset with the verdict, the lead detective says.

Johnson County Lt. Doug Gwinn told The Associated Press the case has hit a dead end after a 20-month investigation into the letter’s shocking allegation of jury tampering failed to identify the author.

The case stems from a three-week February 2016 trial in which parents sued UI Hospitals and Clinics for brain damage suffered by their child during birth. Jurors ruled 7-1 that UIHC was negligent in treating the mother during delivery but rejected the family’s claim that the girl’s injuries could have been prevented had a cesarean section been ordered sooner. Jurors awarded no damages, turning back the family’s request for $10 million or more.

Judge Chad Kepros, who oversaw the trial, received a lengthy anonymous letter days later that claimed to be from a juror. While the letter has been kept under seal, court records show the author claimed to have been offered and accepted a significant monetary bribe in exchange for siding with the hospital during deliberations.

The letter was written by someone with extensive knowledge of the trial, and Kepros requested an investigation into its claims. The plaintiffs, Dale and Jill Todd of Tama, filed a motion for a new trial, citing the letter as possible evidence of juror misconduct.

Gwinn, a sheriff’s office detective who led the investigation, said Thursday he found no evidence that any juror was offered or received a bribe and doesn’t believe that occurred. Instead, he said he believes the letter was a hoax written by someone who was angered by the trial’s outcome and hoping to get the plaintiffs a new trial.

“Based on what the letter read, it didn’t happen,” Gwinn said.

Investigators were able to recover fingerprints from the letter and discover where it had been mailed. Gwinn collected fingerprints from the jurors, the Todds, court officials who handled the letter and others but none were a match, he said.

Gwinn said he was able to rule out the Todds and their lawyer as suspects but that he cannot dismiss the possibility that someone else mailed it on the plaintiffs’ behalf. Still, he added he’s certain that “whoever authored the letter was present during a major portion of the trial” and noted the Todds had no other supporters in the courtroom.

Investigators have focused attention on the juror who dissented from the verdict, but Gwinn declined to call the North Liberty man a suspect. He said only that the man’s fingerprints didn’t match those on the letter.

Kepros said in a recent order that he isn’t ready to accept the state’s conclusion that the letter was a hoax without learning more about the investigation and its findings. He has scheduled a Jan. 26 hearing where Gwinn, jurors and other participants are expected to testify. Kepros intends to rule afterward on whether to grant a new trial or let the verdict stand.

The Todds’ lawyer, Martin Diaz, said the public should wait to hear the testimony before drawing any conclusions about the letter.

The case was rare in that state lawyers representing the hospital went to trial instead of settling, which routinely occurs in malpractice cases that could invite large verdicts.

But Gwinn said he didn’t believe any of the UIHC doctors or lawyers involved had any motive to bribe a juror, noting the verdict would have been paid through insurance or tax funds. Conversely, he said going through a second lengthy trial in the case would be an expensive proposition for them.