Deborah Blum / Los Angeles Times

On April 17, a Pennsylvania physician named Autumn Klein, dreaming of a second child, sent her husband a hopeful text message: “According to my calendar I ovulate tomorrow.”

“Perfect timing,” her husband typed back. And, he reminded her, “Creatine” — referring to the energy drink he’d been mixing up.

“Will it stimulate egg production too?” she asked.

He answered simply — according to a police report — by sending an emoticon, a bright yellow smiley face.

Three days later, Klein, 41, was dead; hospital tests found a lethal amount of cyanide in her blood.

The investigation also found that her husband, Robert Ferrante, 64, a neuroscientist at the University of Pittsburgh, had asked a colleague two days before his wife’s death to order half a pound of cyanide from a pharmaceutical supply company and have it sent overnight to Ferrante’s laboratory — even though he wasn’t using it in his research.

Such pieces of circumstantial evidence — the text exchange, the acquisition of cyanide, tales of a troubled marriage, the telltale blood tests — led to Ferrante’s arrest on murder charges in late July. He’s denied the charges and publicly expressed grief for both his wife’s death and his 6-year-old daughter’s shock and trauma.

In the end, a trial will determine whether Ferrante killed his wife, but whatever is decided, the case opens a window, once again, on the world of homicidal poisoners. I’ve been writing about this subject for more than four years (and, yes, I do worry that my intense interest in the subject makes me seem a little twisted), and I’ve come to believe that poisoners are the coldest of killers.

They plan ahead, they plot out their poison and delivery methods in advance, they entice their victims to consume the poison, and they often stay to watch the poison do its work. It’s true these plots have their vulnerabilities — in the case of Klein’s death, an unusually suspicious doctor ran a test for cyanide after she collapsed and was brought to the emergency room, even though the poison wasn’t part of a standard toxicology screening. Without that, there might not be a case at all. Ferrante had his wife’s body cremated almost immediately after she died.

So, what do we know about poisoners? Most of them believe that careful planning will allow them to escape detection. We also know — or think we do — that “poison is a woman’s weapon.” That’s a direct quote from the 1945 Sherlock Holmes movie “Pursuit to Algiers,” and it’s a familiar literary trope. In George Martin’s “Game of Thrones,” for example, poison is described as the choice of cravens, eunuchs and women. But in fact, most poisoners are men.

The Department of Justice’s report on homicide trends in the United States (1980 to 2008) shows that, of all poisoning killers during that period, 60.5 percent were male and 39.5 percent were female. As psychologist Joni Johnston noted in Psychology Today last year: “Contrary to popular belief, the majority of convicted poisoners are men, overwhelmingly so when the victim is a woman. When the victim is a man, the poisoner is equally likely to be male or female.”

Of course, I’m not arguing away the history of female poisoners. An analysis of British poisoning cases in the 18th and 19th centuries by historian Katherine Watson found that the murderers were fairly evenly balanced between men and women, which is not so far off the statistics seen in our recent DOJ analysis.

My point is, first, to set aside the old myth of poison being a just-for-you-girls kind of weapon, and second, to look more closely at what the numbers actually tell us.

Why are there more male poisoners overall? Because there are more male killers overall.

But I think that fixating on the gender question leads us, somehow, to be dismissive, to miss the more interesting — and more dangerous — issue. Unlike murders by gun, poisoning murders are always premeditated. There’s no sudden impulse, flash of anger or fear, in ordering cyanide so that you can mix it into an energy drink. And poisoners believe that their calculated plans, their cleverness, will allow them to kill and walk away.

They’re wrong about being so clever. Because there’s always someone smarter, such as a suspicious doctor who will surprise the killer by testing for poison in the victim’s blood.

And we’re wrong in our comfortable stereotypes. Poison is not a woman’s weapon, nor a man’s. It’s just an evil one.