What should I do if my friend is detained in Hanyang No.2 Detention Center in Wuhan for intentional homicide? Is it dark inside? Do you want to do something? Can I go and see him?

You can't see him, you can't visit him before sentencing, you can't do anything before sentencing, and life in it is hard. The best way now is to write a letter of understanding to the family of the deceased, and then find a lawyer to defend him and why you killed him. Make it clear to the lawyer. Lawyers will know what to do. Only lawyers can see him now.