Brian Hausler met us in a park about a mile from his house. He was friendly, but I could sense he was enormously stressed. We put a microphone on him, and began to roll tape, as we walked on a cold spring day.

"People keep asking questions," he said. "Did we have an affair? Did I lead her on? There was no affair. I did not lead her on."

Brian is talking about his neighbor, 33-year-old Tina Vazquez. Vazquez is now behind bars, charged with first degree assault for poisoning Brian's wife Angie.

Brian said he and Angie and their two young children moved to Bonne Terre, Missouri, a small town south of St. Louis, about a year-and-a-half ago. Last summer, they became friends with Vazquez, a neighbor. At first, Brian said, she came over with her husband; then they separated. Vazquez soon became a regular visitor, and did some babysitting for Brian and his wife.

At some point last fall, Brian's wife Angie started to have ongoing flu symptoms. Then, earlier this month, Angie got very sick and called 911.

Doctors said she'd been poisoned -- that she must have ingested a toxic substance recently. Angie told her husband that Tina Vazquez had given her an antibiotic capsule about a half hour before the worst symptoms came on. Brian became suspicious, and confronted his neighbor.

"I said, 'What's going on Tina?' And she said, 'I did something bad. I put something bad in Angie's medicine,'" Brian told me.

Police said that "something" was sodium nitrite, a substance used for curing meat. Investigators said Vazquez worked at a meatpacking company, and substituted a toxic dose of the chemical in the antibiotic capsule she gave to Angie Hausler.

"And I asked her why," said Brian. "She just said she thought she could make me happier."

Detectives told us that Tina Vazquez claimed she and Brian Hausler were having an affair, but Brian says that's not true. He says his wife is now home, and recovering.

Brian suspects his neighbor was slowly poisoning her over the course of several months. So far, police allege only one poisoning attempt. But prosecutors say that if she's convicted, Tina Vazquez could face up to life in prison.

Neither Angela Hausler nor Tina Vasquez would speak to us for this story. Tina Vasquez hasn't yet made a plea in this case, and tomorrow (Tuesday morning), she'll make her first court appearance to face formal charges.