This is very sad that no one in your family has talked to you about this and you must find your answers this way.
If you live where the crime was committed, you can go to the local library and look up newspapers during that time. You may also go to the court house and ask them for copies of court transcripts. They will charge for them but it's public records. But someone in your family should surely be able to tell you what happened without covering things up?
I know this helps little but we can not help who our family members are. We only get to pick friends, not family. Being a family member also doesn't mean he is one you want around your kids, as well.
It sounds to me as he killed a child with the offender tag on him.
I hate people that do this. Goes to show the pain goes beyond the victims family and the offenders family also has their burdens to deal with.
I will snoop around some but doubt I will find much.