Religious people present the following objection:

According to religion, if the oppressed victim doesn't get justice in this world against the tyrant, he still knows that Allah will punish the tyrant in the hereafter. But if a child is killed, and police is unable to catch the killer, how that child will get justice in a non-religious system. 

Answer: 

NATURE has no concept of justice and punishment. 

And there is also no 'intelligent design' in Nature, and it does not aim to achieve any goal. 

Due to nature, there are earthquakes, storms, floods, hurricanes which kill thousands of people and destroy whole cities, but nature gets no punishment or reward for all these killings and damage.

Due to nature, Dinosaur and millions of other species were wiped out even before the advent of humans (i.e. so-called Adam) on this earth. There was no goal involved in their coming or becoming non-existent before the arrival of humans. We don't even know about these millions of species which became non-existent before us. 

Due to nature, thousands of diseases come and kill millions of people. And their death is extreme slow and extreme painful. It is hundreds of times more painful as compared to when one person kills another person. So, who is responsible for all this extreme pain and long suffering when a person is killed through these natural diseases, and how to punish the one who is responsible for it? 

And millions of children are born with birth defects and have to suffer the whole of their lives with extreme pain due to this. Who is then responsible, and who should be punished for that? If it was really Allah who gave them these diseases and pain, then shouldn't Allah be punished for this crime? 

Reality is this system of justice and punishment is a man-made system. 

If a killer does not get the punishment, then nature does not care about it. But if he does not get the punishment, then it is a mistake of society, and such a society will get the punishment in this world for this mistake. 

Humans got intelligence due to the process of evolution, and due to this intelligence, they tried to create an 'intelligent design' for themselves, which has an aim and which is based upon a system of justice and punishment. 

And since humans are not 100% PERFECT, thus the system of justice and punishment could also be never 100% perfect. It may be possible that a few criminals may dodge the system and do not get the punishment. But despite these few exceptional cases, our aim as a collective society is still achieved, and we indeed succeed in forming a society which could exist and progress through this system (despite it being not 100% perfect). 

The concept of justice and punishment in the hereafter is only a Drama. No society could be formed on the basis of this concept of justice in the hereafter alone. If it was really possible, then no religious society would have introduced physical punishments in this world. 

And if Islam claims that 'all the actions are based upon (إنما الأعمال بالنيات)', then what about those disabled children who are suffering a painful life, or a person who is mentally disabled and suffering a painful life? They had neither any "INTENTIONS" of choosing this painful life for them, nor they had any "CHOICE". And it is Allah who made them suffer without their intentions and choice. So, without this option of choice and intention, why then any pain and suffering and 'punishment or reward'?