At around 9:30 p.m. on April 14, 2014, Kristine Kirk called 911 to report something wrong with her husband, Richard. For about 30 to 40 minutes, he’d been climbing in and out of the windows of their suburban Denver home, yelling and screaming about the end of the world. At one point, he asked her to kill him.
It was as if he’d lost his mind. There was a gun in the house; Kristine and her three sons were scared, she told the dispatcher. Also, he’d eaten part of a marijuana-laced candy earlier that evening.
Before police could arrive, Richard Kirk had retrieved his gun from a safe. While Kristine Kirk was still on the phone with 911, her husband shot her in the head at point-blank range, killing her.
The killing occurred just a few months after the first legal sale of recreational marijuana in Colorado. Before the shooting, a college student from a nearby state had leaped to his death from a downtown Denver hotel balcony after eating a marijuana-laced cookie.
Although police and prosecutors said Kirk had obvious mental illness and was feuding with his wife prior to her death, opponents of Colorado’s legalization experiment drew an immediate and unsubstantiated conclusion: The cannabis caused it. Kirk himself added credence to the theory by claiming the “marijuana defense,” pleading not guilty by reason of insanity brought on by marijuana-infused candy. (Meanwhile, the very real risk factor of someone with mental instability owning a gun somehow escaped scrutiny.)
On Friday, Kirk pleaded guilty to his wife’s murder, as the Denver Post and Westword reported. By doing so, Kirk spares his children and his dead wife’s family the stress and spectacle of a trial. He’ll also keep marijuana off the witness stand.
About three hours before Kirk killed his wife, he’d eaten part of a THC-laced edible. The edible contained 100 milligrams of THC—a powerful dose, about 10 times as strong as a single-serving recommendation for most users. However, Kirk was not legally stoned: He had only 2.3 nanograms of THC per milliliter of blood in his body.
The murder also followed what had been described as a “rocky patch” in the couple’s 16-year marriage. A few weeks before her death, the pair had had such a bad argument that Kristine Kirk had told a co-worker that she was “scared” of her husband. They were also under financial stress: They had $40,000 in credit-card debt and owed $2,580 to the IRS, a bill due the day after Richard Kirk killed his wife. Prosecutors argued that these factors—not a small amount of marijuana—caused the death.
Science supports that conclusion.
Previous research into the link between drug use and homicide has been far from conclusive. A review published in 1994 entitled “The role of marijuana in homicide” found that out of 268 people incarcerated for murder, about one-third had used cannabis in the 24-hour period preceding the killing—but with so many other factors at play, including the use of other drugs, researchers did not conclude there was a direct causal relationship.
Though researchers have long suggested that there’s some kind of relationship between cannabis use and exacerbated psychosis, the exact link is far from certain.
Recent research has found that “in individuals with an established psychotic disorder, cannabinoids can exacerbate symptoms, trigger relapse, and have negative consequences on the course of the illness.” At the same time, researchers note that “the majority of individuals who consume cannabis do not experience any kind of psychosis.”
Skyrocketing rates of cannabis use across the country haven’t been accompanied by any similar or even noticeable rise in schizophrenia. Even the National Institute on Drug Abuse says that the exact relationship between marijuana and schizophrenia is “unclear.”
As NIDA’s Nora Volkow told NPR, “these studies don’t prove that marijuana use causes the schizophrenia; they only show that people with schizophrenia are more likely to also be weed smokers.”
Though cannabis has been cleared as the culprit, the Kirk murder has had a lasting effect on the cannabis industry in Colorado.
Since the killing, Reason’s Jacob Sullum observed, all edibles sold in the state must follow strict rules. Edibles are limited in strength to no more than 100 milligrams, and edibles must be divided or marked into individually wrapped or easily identified 10-milligram “servings.”
Compare that to other states like California, where despite pleas from within the cannabis industry to limit or regulate super-strong edibles, products containing a debilitating 1,000 milligrams or more are readily available. Still, those edibles haven’t killed anybody. Nor have they been fingered as a factor in anyone’s death.
Meanwhile, there is one substance that’s associated with violent crime, including murder, more than any other. Americans love it, and it’s totally legal—alcohol, of course.
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