A 10-year-old Florida girl was beginning her first day of online school when her mother was shot to death by her ex-boyfriend at their home, investigators said Tuesday.

Donald Williams, 27, shot and killed 32-year-old Maribel Rosado Morales in front of her four children and their two cousins at her Indiantown home, Martin County Sheriff William Snyder told reporters at a press conference, which was recorded by WPEC-TV.

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The shooting unfolded during an argument after Williams entered the home around 8 a.m. and confronted Rosado Morales about an online video, Snyder said. Williams shot her multiple times and fled the home.

Williams was taken into custody after he tried to flee on board a bus, investigators said. (Martin County Sheriffs Office)

The 10-year-old girl's teacher at Warfield Elementary School witnessed the incident while setting up the class ZOOM call, Snyder said.

"The teacher's online — I've never done a Zoom with children, so I'm picturing there's other children on — and the teacher can see the children," he said, adding that she "heard a commotion, heard profanity, realized it was some sort of domestic altercation.”

"The teacher said she mutes her button [so] nobody has to hear it, and then she sees the 10-year-old put her hands up to her ears," Snyder said.

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He said the student's end of the Zoom call cut out almost immediately after the child covered her ears. A bullet had struck the computer.

No children were injured during the shooting.

Williams fled the scene on a bicycle before boarding a bus. The bus driver was suspicious and called 911, WPTV reported. A SWAT team in the area responded and took Williams into custody.

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Williams confessed to the shooting and will face a charge of first-degree murder, Snyder said.