Police spokesperson Lieutenant-Colonel Dimakatso Mooi said the family lived on a dumping site after their father was sentenced to life behind bars for killing their mother.
Jan Bester, the accused, had been a friend of the boy's family.
Mooi said Duiker's body was discovered next to a railway line on August 25 last year.
"The Duiker family was adopted by the De Aar Police in 2014 after it was discovered that they were living at the dumping site after their father was sentenced to jail for murdering their mother".
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Mooi said "different stakeholders" built a home for the family and furnished it.
The Cluster Commander of Pixley Ka Seme, Brigadier Sofika, applauded the investigating officer and welcomed the sentencing.
“By killing the children we are destroying the future and those who kill them do not deserve to live in the society. May this sentence sends a strong message to other perpetrators that killing of children will not be tolerated by the police”.