Is the repentance of a young man who witnessed a murder in his childhood but did not report it—then innocent people were imprisoned because of it—valid, and what must he do now that he has repented?

It is not permissible to conceal truthful testimony, and the obligation to render it becomes more emphatic if its concealment leads to the loss of a Muslim's right. However, if the witness fears harm to himself, his property, or his family, then he is not obliged to render it, based on the Almighty's saying: "And let no scribe be harmed or any witness," and the Prophet's (peace be upon him) saying: "There should be no harm or reciprocating harm." Testimony is not obligatory if the ruler is unjust. If you are safe and the judge is just, then it is obligatory for you to render the testimony.