The Colchicine Poisoning of Mary Yoder: Did Investigators Convict the Right Person?

In July 2015, 60-year-old chiropractor Mary Yoder appeared to be in excellent health. She ran a successful family practice with her husband, Bill, in Whitesboro, New York, and was known for her interest in nutrition, supplements, gardening, and healthy living.

Then, without warning, Mary became violently ill.

What initially looked like a severe stomach bug quickly became something much more serious. Mary suffered relentless vomiting and diarrhea before being admitted to the hospital. Her condition continued to deteriorate, and on July 22, less than 48 hours after her symptoms began, she died following multiple cardiac arrests.

Doctors couldn’t explain how a seemingly healthy woman had declined so quickly.

A Rare and Deadly Poison

During Mary’s autopsy, the pathologist discovered extensive damage throughout her body. Her organs reportedly looked as though they had been subjected to aggressive chemotherapy, even though Mary had never undergone cancer treatment.

Initial testing for common poisons—including arsenic and cyanide—came back negative. But several months later, a poison-control expert suggested testing Mary’s samples for colchicine.

Colchicine is most commonly used in small, carefully controlled doses to treat gout. It also has agricultural applications involving plant breeding. Because the difference between a therapeutic dose and a fatal one is extremely small, an overdose can cause catastrophic organ failure.

Testing reportedly revealed enough agricultural-grade colchicine in Mary’s body to kill her many times over.

Her mysterious death was now a murder investigation.

An Anonymous Letter and a Bottle Inside a Jeep

Investigators initially examined Mary’s husband, Bill, but found no life insurance payout or other obvious financial motive. Although Bill began dating Mary’s sister, Kathy, shortly after Mary died, a review of their electronic communications reportedly found no proof that their romantic relationship had started beforehand.

Then, in November 2015, investigators received an anonymous letter accusing Mary and Bill’s son, Adam, of the murder.

The writer claimed Adam had confessed to poisoning his mother and revealed exactly where police could find the remaining colchicine: underneath the passenger seat of his Jeep.

When investigators searched the vehicle, they found a bottle of colchicine exactly where the letter said it would be. Beside it was a receipt containing an email address that appeared to belong to him: MrAdamYoder1990@gmail.com.

But Adam denied everything. He said the email account wasn’t his and insisted someone had planted the evidence. He also had an alibi: He had been visiting his sister on Long Island when his mother was believed to have been poisoned.

If Adam was telling the truth, someone had carefully framed him—and then directed police straight to the planted evidence.

The Evidence Against Katie Conley

Investigators turned their attention toward Adam’s former girlfriend, Kaitlyn “Katie” Conley, who worked as the office manager at his parents’ chiropractic practice.

Katie initially denied knowing who wrote the anonymous letter. During a later interview, however, she admitted writing it. She maintained that Adam had confessed to her and said she had been afraid to come forward because of their turbulent and allegedly abusive relationship.

Digital forensic evidence soon complicated her story.

Investigators determined that the Gmail account used to order the colchicine had been created on the computer Katie normally used at work. The account was also connected to her phone and home computer, and its password was reportedly “Adam is gay.”

The colchicine had been purchased using prepaid cards bought in Adam’s name, but surveillance footage reportedly showed Katie purchasing the cards. One card’s serial number matched the number on the chemical company’s receipt.

DNA testing provided another major piece of evidence. Adam was excluded as a contributor to the DNA found on the colchicine bottle and its cardboard packaging. Katie, however, was identified as a major contributor.

Katie was arrested and charged with second-degree murder in June 2016.

Two Trials and Two Different Outcomes

Prosecutors argued that Katie poisoned Mary either to punish Adam for their breakup or to create a tragedy that would bring them back together. They believed she placed the colchicine in a protein drink Mary consumed at work.

Katie’s defense challenged that theory and pointed toward other possible suspects, including Bill and Adam. Mary’s hospital records also complicated the alleged method of poisoning: They reportedly documented Mary eating a protein bar for lunch and grilled chicken for dinner, with no mention of a protein shake.

Katie’s first trial ended with a deadlocked jury and a mistrial.

At her second trial, jurors were allowed to consider first-degree manslaughter as a lesser-included offense. In November 2017, they acquitted Katie of second-degree murder but convicted her of first-degree manslaughter. She was later sentenced to 23 years in prison.

Katie continued to insist that she was innocent.

A Conviction Overturned

In January 2025, a New York appellate court overturned Katie’s conviction after concluding that her attorney had provided ineffective representation concerning evidence recovered from her cell phone.

The defense argued that investigators had exceeded the scope of the warrant used to search the phone—one of the most important sources of evidence against her. Katie was released the following month after spending approximately seven years in prison.

Her release did not establish that she was innocent. It meant that the court determined her conviction had been obtained through a legally flawed process.

The prosecution has continued its efforts to pursue the case, leaving Katie’s legal future uncertain.

What Does the Forensic Evidence Really Prove?

The forensic evidence in Mary Yoder’s case answered one crucial question: Colchicine killed her.

But other questions remain much harder to answer.

Katie’s DNA showed that she had touched the bottle and its packaging—but it could not establish precisely when or why she touched them. Digital evidence connected her devices to the email account used to purchase the poison—but the legality of the phone search eventually helped overturn her conviction. Toxicology identified the murder weapon—but investigators never definitively proved how or when Mary consumed it.

Was Katie responsible, as prosecutors argued? Was Bill overlooked too quickly? Or could Adam have played some role despite his alibi?

More than a decade after Mary Yoder was poisoned, her family remains divided, Katie’s case remains legally unsettled, and the most important question continues to linger:

Who really killed Mary Yoder?

Listen to the full episode of Forensic Tales for the complete story and a closer examination of the forensic evidence at the center of this controversial case.