Wendy Bellar tried to leave the home with two of the children after a fight with her husband, Polk County Sheriff's Department spokesman Scott Wilder said in a statement.
But Troy Bellar opened fire with a 7.62 mm rifle and killed his wife, 5-month-old Zack James Bellar and 7-year-old Ryan Patrick Bellar in the front porch area.
Another son, 13-year-old Nathan Bellar, was pursued through the garage by his father, evaded several gunshots, and made it safely to a neighbor's house. The boy was being placed with family members.
Investigators were still trying to determine the sequence of the shooting.
No neighbors were injured by gunfire, according to a canvass by deputies.
"You don't have stuff like that in this neighborhood," neighbor Tammy Womble told The Ledger newspaper in Lakeland.
"It was just gunshots going off. We didn't hear screams or anything," she said.
Wilder said the husband had been arrested twice in the county, on suspicion of aggravated assault in 1994 and suspicion of driving under the influence in 1999. Wendy Bellar was arrested in March on suspicion of domestic battery.
"This is one of the most tragic, senseless and horrific crimes we have investigated," Sheriff Grady Judd said in a statement.
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