Her sentencing is set for 10 a.m. Feb. 26 in Judge James Hartenbach's St. Louis County courtroom.
Barlow was charged with first-degree murder and armed criminal action in the shooting death of Michael Strong on July 27, 2007. Barlow was arrested Aug. 1, 2007.
In exchange for the guilty plea, the state agreed to amend the first count to second-degree murder and allow a cap of 25 years in prison and the chance of parole after serving 85 percent of her sentence.
As part of the plea agreement, Barlow supplied police with a map that led to the recovery of the murder weapon missing from Strong's home the night of the shooting. Gray said the weapon was found Friday in a road ditch less than a mile from the Strong home.
Gray said it was clear within hours of Michael Strong's murder that one person acting alone had committed the crime.
"[Michael Strong was] a fellow who carefully locked his doors every night, where [Barlow] kept at least two dogs in the house, which barked at everyone, friend or foe," Gray said. "The fact that the shooter was able to move through the house that night, get his gun and set the lamp out of the way to set the shot without waking him up -- there's not any possibilities left except Lisa Barlow. Those dogs had a part in showing who the killer was because they don't know how to lie."
He said a delay of nearly 90 minutes between when the shooting happened and when Barlow called police was another factor. Statements gathered during the initial investigation revealed that Barlow was unhappy in the relationship and had been having an affair with her ex-husband. Police interviewed that man but he was not considered a suspect in the shooting, Gray said.
The Bollinger County prosecutor communicated frequently with Michael Strong's family during the case, including explaining plea-agreement negotiations. He said the family "was pleased with the county's ability to recover the gun" and was supportive of the plea agreement.
"They're interested in making sure something does happen and she does get punished. They have some questions they hope get answered at the sentencing. We got most of the way there today."
A relative of Michael Strong who did not want to be named said it has been "a terrible year and a half" for the family.
Public defender Amy Metzinger, who represented Barlow in the case, said she had nothing to add to what was included in Gray's announcement Monday.
Bollinger County officials had been bracing for the costs associated with an out-of-county trial, expecting to spend as much as $30,000. But that's not what Presiding Commissioner Wayne Johnson focused on when he reacted to the news.
"You want justice done and justice served and hopefully that's what was done," he said.
Barlow's plea agreement spares Michael Strong's family the added grief of a trial that could have lasted two weeks, Gray said. The deal also gives Strong's family more information than might have been revealed if the case had gone before a judge, because Barlow may not have testified.
"There's a finality you don't always see in trial cases," he said. "It's going to be good for them, in their minds, that she's taking responsibility, that she's going to be punished, and they have a pretty good idea for how long. So they see justice is being served."