It has always been my (completely unfounded) feeling that they were ambushed and killed, then weighted down somehow and dumped in the Delaware. Never heard of this Robert Carey character till now, but apparently he lived in Palmyra, NJ, and "worked" (by worked I mean sold drugs) in Philadelphia along the river, from Port Richmond/Fishtown (where it sounds like he may have grown up) to South Philly (where missing couple were last seen). He also sounds pretty violent from the newspaper articles I've read. It's possible he followed and confronted the couple (were they abusing prescription pills? Is it possible one or both of them owed him money?), killed them, then weighed their bodies down in the river (growing up along the Delaware I'm sure he was familiar with some isolated areas where he could do this and not be noticed), and brought the truck to a chop shop. There are PLENTY of illegal chop shops or parts shops that will not ask questions, and a big time Philadelphia drug dealer I'm sure had connections within one or many of them.
The reason I keep coming back to bodies being in the river is because I cannot imagine that if they were dumped on land somewhere they wouldn't have been found by now. It's been eight years and is such a high profile case.
So is there any evidence that Richard or Danielle were using drugs? Were either of them involved in anything illegal that maybe got them into hot water? Did either of them have court cases coming up? I think I remember Danielle was in the process of a divorce--is it possible she would have wiped her husband out financially? I have a weird feeling that this disappearance had something to do with money--and not so much making money, but protecting money that was already made.