Advising someone in this situation is a complex and morally challenging task. Here are a few considerations and potential courses of action your best friend could take:

1. Speak to a Therapist or Counselor: First and foremost, your friend should consider speaking to a therapist or counselor to help them process the guilt and emotions they have been carrying for so long. This can provide them with a safe and confidential space to discuss their feelings and possibly find a way to cope with their past actions.
2. Legal Consequences: Your friend should consult with a legal professional to understand the potential legal consequences of their actions. While the homeless person accused of the crime has passed away, there may still be legal repercussions for your friend, depending on the circumstances and the laws in their jurisdiction. It’s important to understand the legal implications before taking any action.
3. Confession: If your friend is determined to come clean, they should consider the consequences of their confession carefully. Confessing to a crime committed many years ago can have severe consequences, both legally and personally. They should be prepared to face the legal system and the impact on their family, as well as potential public backlash.
4. Anonymous Reporting: If your friend feels a strong moral obligation to ensure justice is served, they could anonymously report the crime to law enforcement. However, this option is not without risks, as it may still lead to an investigation and potential legal consequences for your friend.
5. Seek Forgiveness: If your friend doesn’t want to involve the legal system but seeks redemption, they might consider other ways to make amends. This could involve volunteering, contributing to charitable causes, or dedicating themselves to helping others in need. Seeking forgiveness and trying to make the world a better place can be a way to find some form of redemption.
6. Consider Family: Your friend should weigh the potential impact on their family and loved ones carefully. A confession could have devastating consequences for them, and your friend should think about how they can best protect their family’s well-being while still addressing their own guilt.

Ultimately, the decision your friend makes should be based on their own values, conscience, and willingness to accept the consequences of their actions. Encourage them to seek professional advice, both legal and psychological, to make an informed decision that aligns with their beliefs and priorities. It’s a deeply personal and challenging situation, and there may not be a perfect solution.