All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
First of all, we thank you for asking about religious matters that are of interest to you, and for being keen on ridding yourself from accountability in regard to the rights of the people.
These materials whose owners indicated that their rights are reserved, must be preserved and not transgressed except with the permission of their owners. The Islamic Fiqh Academy issued a decision to this effect. However, some scholars are of the view that it is permissible to benefit from them for one’s own personal use, i.e. not to make a profit from them or to trade in them. This is a considerable view. Therefore, we hope that there is no sin on you for what you have done in this regard.
If you have used any of them to make a profit, then you have to repent. Their owners have a financial right upon you according to benefits they miss out on because of you, and according to the damage caused to them because of this unauthorized usage.
What is important is that you return the right to them even if it is in an indirect way; i.e. you do not have to inform them about transgressing their rights.
On the other hand, we do not know what you mean by saying: “I stole a lot of things.”; are you referring to the usage of these materials, or did you steal money from the people?
In any case, in order to achieve sincere repentance from any financial right, you have to give back the right to their owners. If you are unable to find their owners, then you should donate the money in charity while intending the reward for them. Afterwards, if you find their owners, then you give them the choice either to return their rights to them or for them to accept the charity on their behalf.
We advise you to do good deeds as much as possible, seek Islamic knowledge, attend circles of virtue, and keep company with righteous women. This will help in doing good, becoming righteous, and staying steadfast on the right path.
Allah knows best.