The boyfriend and the mother were a couple of abusive, violent, drug addled creeps who are so powerless over their own lives, that they take their frustrations out on little children, and hurt those who are powerless to defend themselves.
In the beginning I read where the mother had just come home from work (I want to say it was after 9:00 PM). This would mean that she came in a vehicle around that time (the red SUV they towed away). Could she and he have come in together after taking the body over to that house? The people were out of town. Maybe the boyfriend's brother, who is good friend's with the people who live in that house - got the stolen SUV and got rid of the body sometime during that week - because the police didn't go over to look at that house until the following weekend.
I'm sure mother and boyfriend thought dumping Robert's body in a canal, and not having him discovered for a week or so would disfigure his body enough to make the cause of death difficult to determine. Once a body has been in water that long, bruising, cuts, etc, are probably indistinguishable, or impossible to determine if they happened before or postmortem (from making it's journey down a canal with debris in it).
Mom and boyfriend are betting on there not being sufficient evidence to charge them with murder. I fear there is too much room for reasonable doubt now that it has been determined that a body could float the distance from their apartment to where his body was discovered (it was quoted in an article, that it is possible, grates and all). I know this case is getting a lot of national attention, maybe the authorities will bring in Dr. Michael Baden (from the HBO series Autopsy) or someone like him to get their professional input. If it is murder, please God, don't let who did it get away.