THONOTOSASSA, Fla. (WFLA) — A 24-year-old Florida mother is accused of murdering her toddler son, authorities said.

Rebecca Gussage-Johnston told deputies the 2-year-old acted out and she punished him, according to the arresting officer’s report.

The report said Gussage-Johnston told deputies she watched her son take her his last breath and die in her arms. Gussage-Johnston did not call 911, despite having a working phone.

Deputies said a concerned family member called authorities to report a toddler in distress.

“This is just a case that’s just as heartbreaking as it is disturbing,” said Phil Martello, with the Hillsborough County Sheriff’s Office.

Family confirmed Gussage-Johnston lived in an RV on a commercial property along U.S. Highway 301 with her 2-year-old son Eli, her 8-month-old daughter and their father.

“When they arrived, what they saw was horrific,” said Martello. “They saw a child strapped to a chair — signs of extreme neglect abuse — and despite their best efforts, they were not able to save this child.”

The report said the child had suffered head trauma, wounds and bruising, and that Gussage-Johnston admitted to leaving him there for more than 15 hours because he was acting out and screaming.

The next morning, the mother told authorities she found her son flipped over and watched him “suffer from seizures and shaking uncontrollably,” according to the report.

Deputies said Gussage-Johnston was initially arrested on May 19 for aggravated child abuse resulting in great bodily harm and child neglect. The Medical Examiner’s Office ruled the toddler’s death a homicide because of severe neglect. Gussage-Johnston is now facing an additional charge of murder in the first degree while engaged in aggravated child abuse.

“[Hillsborough County] Sheriff [Chad] Chronister wants to make it clear that we will not tolerate anything like this happening to a child,” said Martello. “There’s never an excuse to do this to a 2-year-old child.”

Family told News Channel 8 that Eli’s 8-month-old sister is now in the care of her grandfather.

“We know that every parent has gotten frustrated, but we’ve kind of helped her with some tools and tips and tricks to help to deal with those frustrations so that child wouldn’t of had this awful ending,” said Nikki Daniels, with Champions for Children. The organization’s mission is child abuse prevention.

The organization provides education through programs and services to families, especially those who are struggling or at risk. Champions for Children offers classes from prenatal to parenting all for free. Daniels said 1 in 4 kids in Hillsborough County are victims of child abuse or neglect in their lifetime.

“For us it’s about attachment and bonding, because if we can help parents attach and bond to their children, and then give them the tools, they need child abuse is much less likely to happen,” said Daniels.

She said each year, her team helps more than 30,000 people in the Tampa Bay area.

If you believe a child is in danger, you can call the abuse hotline at (800) 96-ABUSE to report it.