The child died of a self-inflicted wound in what the Los Angeles Police Department is investigating as an unintentional shooting.
A family friend said the gun belonged to a licensed security guard who visited the home and said the gun had been hidden in a closet. LAPD has not confirmed that the security guard's weapon was the one found by the boy.
According to friends and family members, Justice was under county Department of Children and Family Services supervision, as were his four siblings.
All have lived at the home since they were babies because their birth mother was unable to care for them.
Neighbors created a GoFundMe page to raise funds for the child's funeral.