I think that if the child got into some drugs and accidentally died of an overdose that the boyfriend would have cracked a long time ago and given up the location of the body. The fact that he won't even under enormous pressure leads me to believe that the baby was beaten to death.
If it was an accident and the boyfriend admits he messed up by trying to cover up the crime and tells them where the body is, then surely things will go better for him.
If there is evidence all over that child that he was beaten to death then it is better for the boyfriend in the end if the body is never found.
Sadly this is why I do not think the cause of death was an accidental drug overdose.
He could of caught little Lonzie getting into the drugs and then beat him ....I still think some how drugs are involved in this whole case. Two adults and 2 little kids in 1 bedroom is very very tight....and more then likely these so called adults where not too good at keep things picked up or clean and just dumped stuff all around even their drugs. Doesn't take much time for a little one to grab a piece of drug he thought was candy ..shallow ...BF see it happen and BF goes off on child.