Who caused the maria hertogh riots?

There was already racial tension then. Maria was born to Dutch Catholic parents and yet was raised by a Muslim, Aminah binte Mohamed. Both her biological parents and her guardian wanted to keep her. She was named Nadra binte Ma'arof by Aminah, and was also married off to a Malay.

A legal battle for the custody of Maria Hertogh followed, and photographs in newspapers of a Muslim girl in a Catholic convent and claims that she had bowed down to the Virgin Mary affected religious sensitivities and whipped up emotions. At the appeal hearing on 11 December 1950, the Judge dismissed Aminah's appeal and custody was given to Adeline Hunter, her biological mother. Upon hearing the judgement, huge crowds outside the court rioted, convinced that the colonial laws, the courts and the legal system were prejudiced against Muslims.

For three whole days, mobs of Malay and Indian Muslim rioters attacked any European and Eurasian in sight, setting up barricades along major roads, cars and houses on fire and taking control of districts in the vicinity of Sultan Mosque, North Bridge Road and Jalan Besar. Rioting was stopped only after two troops of the Internal Security Battalion were called in, supported by several Malays within the troops. Even so, scattered attacks continued over two days. A 24-hour curfew had to be imposed for two weeks before British and Malay troops and the Constabulary regained control of the situation.

Altogether, 18 people were killed and 173 were injured. Nine were killed by rioters while the others were killed by policemen. Aside from a Police Inspector and a Special Constable, those killed by rioters had little to do with the Hertogh case and their murder was motivated more by fanaticism and racial hatred.