Mackenzie then started to attack his mother, hitting her multiple times with the weapon. His adult stepsister started screaming, causing his father to enter the room and witness the attack, investigators said.
Mackenzie then attacked his stepsister when she tried to run out of the room. His father was unable to stop the attack and ran from the house to call 911.
Officers arrived and took Mackenzie into custody.
The mother was pronounced dead at the scene. The stepsister was taken to a hospital where she was pronounced dead, investigators said.
The identities of the victims will not be released under a Florida law that protects victims.
Mackenzie was arrested and charged with two counts of first-degree murder, according to arrest records.
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