The trial of a Florida woman accused of plotting the murder of her husband in 2000 and marrying his killer, with whom she was said to be having an affair, began Tuesday.

Denise Williams, 48, is facing a first-degree murder charge in the suspicious death of her husband, Mike Williams, who had disappeared while duck hunting on a large lake near Tallahassee nearly 20 years ago. Investigators said they initially believed he fell from his boat and alligators ate him.

However, years later his best friend and insurance agent, Brian Winchester, confessed to the killing, adding that Williams’ wife was in on it. Investigators ultimately concluded the man had died from a shotgun blast to the head and had been buried near the lake.

Winchester testified Tuesday about his relationship with Denise Williams. He claimed Mike Williams apparently was growing suspicious about her activities. Winchester said that suspicion and the fact that one of Mike Williams' insurance policies was about to lapse led him and Denise to kill him. "We knew our window of opportunity was closing," Winchester testified.

Philip Padovano, one of the attorneys representing Denise Williams, said there was no proof his client was having an affair with Winchester or had helped plot the killing. "There's no tangible evidence or physical evidence to connect Denise Williams to this crime."

Winchester said he had intended to drown Mike Williams by pushing him from his canoe, but panicked when he saw Williams struggling in the water to get out of his jacket and duck waders and shot him. He said he dragged Williams' body back to shore, put him in his truck and buried him hours later.

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At the time of his death, Williams had three life insurance policies worth $1.75 million. Denise Williams initially petitioned to have him declared dead due to accidental drowning because crews hadn't found the body. She married Winchester in December 2005, but the relationship soured and they divorced in 2016.

Last year, Winchester pleaded no contest to kidnapping his ex-wife at gunpoint, and was sentenced to 20 years in prison. The very next day, officials announced that Mike Williams' remains were found at the end of a dead-end road after they received "new information." The body had been discovered two months earlier, but the state's Department of Law Enforcement needed to confirm through DNA tests that it actually was Williams.

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The woman’s defense team told the jury: "You will have to rely on the word of a murderer and a convicted felon."

She also faces charges including conspiracy to commit murder and accessory after the fact.

The Associated Press contributed to this report.