There is DNA evidence to back up the claims of the police in this case. Also, there is a lot of evidence the police ignored during the original investigation because they were fixed on the parents as guilty. They weren't, there was no evidence at all of the parents committing this crime regardless of years of police probling, lying and manufacturing evidence.
They also covered up evidence that would have led to the arrest of this guy years ago because they wanted to nail the parents. They were blinded to the real facts by their training that relatives are the perps in most murder cases.
All this is a matter of record, with the DA that was in charge at the time saying recently that he tried to get the police to investigate the other evidence to no avail. His statement is long and very damning to the police.
But, not to worry, everything will come out in the end.