Must I return the price of eight computer memory sticks I took from a non-Muslim company, knowing that I thought they would not benefit from them and that I needed them, and must I mention the reason or spend it on Muslim interests?

Disbelief alone does not permit taking the property of the one who holds it. Stealing the property of dhimmis, mu'ahids (those with whom there is a treaty), and musta'mins (those granted safe conduct) is Islamically forbidden by scholarly consensus. The sin increases if the thief was entrusted, for Allah Almighty says: "O you who have believed, do not betray Allah and the Messenger or betray your trusts while you know." (Quran 8:27). A person's lack of need for his wealth does not make it permissible for others to take it without his permission, for Allah Almighty says: "O you who have believed, do not consume one another's property unlawfully but only [in lawful] trade by mutual consent." (Quran 4:29). Therefore, repentance is obligatory, and the stolen money must be returned to its owner or his agent without mentioning the reason. It is not permissible to spend these stolen goods for the benefit of Muslims as long as it is possible to return them to their owners.