A Wisconsin couple have been charged with plotting to stalk and poison two women whom the man had previously dated, using cyanide, homemade poisons and other substances, authorities said.

The couple, Paul VanDuyne Jr., 43, and Andrea Whitaker, 41, both of Madison, were charged with attempted murder, stalking, aggravated battery and recklessly endangering safety, the Wisconsin Department of Justice and the Police Department in Middleton said in a statement Friday.

According to court documents, Rock County sheriff’s deputies were dispatched to a hospital May 12 to investigate a possible poisoning.

Over the next five weeks, they conducted an investigation with the FBI and other agencies and found that VanDuyne and Whitaker had “conspired to gather or create elaborate poisons” in an attempt to kill two women, court records show.

One of the women began noticing the effects of a poisoning attempt on or around April 26, when the authorities say she noticed that a water bottle in her gym bag had a “rancid” taste. The water caused the victim, who was not identified in court records, to throw up. In a separate incident in June, she was hospitalized for severe abdominal pain. Doctors found a large amount of thallium in her system, according to court documents.

Investigators found that the woman’s car had been broken into, and that her gym water bottle was laced with thallium and cyanide, authorities said. Thallium, which was once used in rodent poisons, is a “tasteless and odorless” substance that has been used in murders because it is difficult to detect, according to the Centers for Disease Control and Prevention

The victim’s mother told investigators there had been other “suspicious incidents” before the hospitalization, including a sulfur smell in her vehicle and “a sand-like substance” on the driver’s seat. That substance turned out to be abrin, a potentially fatal toxin derived from the seeds of rosary peas, according to testing cited in court documents.

When investigators asked who could have possibly poisoned her, the victim could not immediately think of anyone but later named VanDuyne, whom she had met two years earlier on a dating site and dated casually. The relationship ended when VanDuyne said he had begun seeing a woman who was finishing pharmacy school and who would be moving to the area soon, according to the victim.

The victim told investigators that after months of no contact with VanDuyne, he began sending texts earlier this year in which he accused her of being evil and blamed her for causing his girlfriend to kill herself after she found out about their relationship. The girlfriend was later identified as Whitaker, who is alive.

In another episode in Middleton on May 15, police responded to a call about someone attempting to break into a different woman’s car at a Costco. The woman told officers that nothing had been stolen, but that the water she had left in the car tasted “awful” and made her mouth feel numb.

A witness told the police that a man, later identified as VanDuyne, had rummaged through the car before driving off in a minivan with a license plate matching that of a vehicle registered to VanDuyne.

Days later, police were called when a man tried to break into the same woman’s car outside the Costco, according to court documents.

When Middleton detectives reached out to the car’s owner, who was not identified in court documents, she told them that she knew VanDuyne and that they had gone out on a few dates more than a year earlier. She said she ended the relationship because she was not interested in him, according to court records.

The woman told investigators that she had not heard from him lately but that he knew where she lived and what kind of car she drove.

While speaking to an officer, the victim said her boyfriend had also recalled seeing “a strange woman” who had appeared in her garage the previous month.

When he approached the woman, she left the garage and the couple then followed her to confront her. She denied having been in the garage, court documents show.

When detectives searched VanDuyne’s house and minivan in June, they found glass vials; rosary peas, which are a natural source of abrin; and a seed grinder, according to court documents.

After his arrest, VanDuyne called Whitaker from the Dane County Jail and gave her instructions to remove “the cat stuff” from the laundry room along with cat medicine and garbage from his home.

In a second call, he asked her to remove a laptop computer from his house, according to court documents. After she left his residence, authorities found she had a laptop, a garbage bag and a cloudy vial of liquid she described as “cat medicine.” She was arrested at the scene.