The fixer

Your favorite sibling confides in you that he accidentally hit somebody with his car while driving on a country road 10 years ago. He "thinks" the person was "probably ok" but he's not sure. He has since married and now has 2 kids. Do you call the police to report the accident?

— Tentative Apologist (@RandalRauser) March 25, 2019

i) To begin with, it seems unlikely that the police could link your sibling to a hit-n-run from ten years ago. How could they establish that your sibling was there at that precise time and place? Unless he still owned the car and there was still trace evidence, what is there to connect a particular driver to the crime?

It's unlikely that the driver will confess, unless they lie to him about what they know. So confronting him is pointless. He will deny the crime. 

ii) What exactly could your sibling do at this stage to restore the victim–assuming he was seriously injured (much less killed)? 

iii) Since you're not responsible for what your sibling did, are you responsible for turning him in? This isn't an ongoing thing, as if he's a career criminal. This isn't about preempting a future crime, as if your sibling threatens to go on a shooting rampage. 

iv) A problem with Rauser's poll is the forced options. But consider another option: suppose, by comparing news reports with what my sibling told me, I'm able to ID the hit-n-run victim. Suppose I make discreet inquires to find out how he's doing. Suppose I'm in a position to befriend him and help him out in certain ways. I never tell him about my relation to the perp. I just make this seem like a random friendship. I'm vicariously making restitution for my sibling's crime. I'm the fixer. That might be more productive than reporting my sibling to the police.