The stories described women meeting violent ends at the hands of their exes: slowly poisoned by asbestos or locked in a submerged box.

In real life, authorities say, the man behind those tales was plotting an equally disturbing attack. Consumed by rage and resentment after a breakup, Jason William Siesser used bitcoin for a dark-web purchase of a chemical toxic enough that a few drops could kill. In poems discovered inside his home, the former Missouri teacher and group home worker described being overwhelmed by hatred toward a woman who broke off a relationship with him.

“Letting go of anger is the right thing,” he wrote, according to prosecutors. “But it makes me feel so strong I dream about your ending/ You burn up in flames/You suffocate on your own blood/Your soul completely drained.”

The 46-year-old Columbia, Mo., man was sentenced Tuesday to 12 years in federal prison after pleading guilty to attempting to acquire a chemical weapon and identity theft. The sentence came after he admitted to making the 2018 purchase while using the name of one of two juveniles the state had placed in his custody, in hopes of avoiding detection.

The amount that he chose to buy, prosecutors said, was capable of killing as many as 300 people.

In an interview Wednesday, Siesser’s attorney, Christopher Slusher, said his client had “expressed tremendous remorse” for his actions. He said Siesser, a former member of the military who had served overseas, had never before gotten in trouble and was reeling from mental health issues at the time he sought out the toxic chemical.

“He understands why people might see this differently, but he doesn’t believe in his heart he would have gone further with anything,” Slusher said.

According to federal court records, Siesser’s first attempt at getting his hands on the chemical came in June 2018. An affidavit filed by prosecutors redacted the name of the substance he was seeking. But once the text of the filing was pasted into another document, it identified the chemical as dimethylmercury, a rare organic mercury compound.

The danger of the colorless liquid was demonstrated in the highly publicized 1997 death of Karen Wetterhahn, a Dartmouth College professor. The 48-year-old scientist had been using the compound to study the effects of toxic metals on human cells when a few drops spilled onto her latex glove. She died of mercury poisoning 10 months later.

Siesser told investigators he had read an article about a scientist who died after exposure to the compound; it was not clear from court documents whether he was referring to Wetterhahn. He said he had initially tried to get it from a legitimate chemical supplier, telling the seller it was for “a gifted chemistry student.” But lacking the required permit, he was rejected.

In July of 2018, he sent bitcoin to an Internet seller after acknowledging that he understood the chemical posed a risk of death to anyone who came into contact with it. When it didn’t ship, Siesser told the seller, “I plan to use it soon after I receive it. I don’t really have any concerns. If you have any tips or care to offer advice feel free.”

He tried again a month later, paying the equivalent of $150 in bitcoin. This time, authorities intervened with an undercover operation. He signed for a package on Aug. 23, 2018, believing the toxic chemical was inside, authorities say.

Officers knocked on the door after watching Siesser accept the delivery.

He told the authorities that he bought a speaker, but then he later said in an interview that he purchased dimethylmercury using the names of the minors in his care. Although he told investigators that he had bought the vials for experiments related to bio-hacking, a form of gene editing through protein manipulation, he could not explain how the evolving science worked.

One of the juveniles told officers that Siesser said he wanted to be an assassin and kill those who wronged him, including an ex-wife, according to the affidavit. The woman, and another woman with whom he went on three dates and felt a strong connection to, “left him heartbroken,” prosecutors said.

When authorities searched the home for what Siesser thought was dimethylmercury, they found other substances, including cadmium arsenide, a toxic compound. They also found his writings, which prosecutors said “articulated heartache, anger, and resentment over a breakup and a desire for the unidentified cause of the heartache to die.”

“Right now your happy,” he wrote in one entry. “But that won’t last/ My anger is coming/And you won’t die fast!”

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