The boy's mother was arrested more than 25 times on charges including fraud, theft, drugs and prostitution.
He was entrusted to the care of his grandmother, who got drunk and angry most nights at their West Boynton Beach home, he and his family members told deputies.
The 14-year-old now stands accused of killing two men, shooting them each in the head. One sold him drugs and often flaunted large sums of cash, the boy told investigators. After the April 7 killings, the boy went on a shopping spree the same day at two malls with his friends, deputies say.