Sorry, I'll try that again.
It isn't that easy to make a full size P/U disappear. Sure, a connected hit man could just turn it over To some mob owned w shop. The trouble is that everyone who works there is going to wonder about a perfectly good truck being broken down. The publicity about the disappearances and reward offers start coming in. Someone is going to get a bright Idea and come forward. Same principle any way a hit man might turn a truck over to a third party to "get rid of": it would be giving information about a murder you committed to someone with no culpability in that murder. They could use that information for blackmail, a reward or a get out of jail card. It is something a Pro just wouldn't do.
Putting the vehicle in water isn't that easy either. A car that goes off the road into water accidentally is often going at a high speed and will travel away from shore into deeper water or current. If you push a vehicle into water, perhaps off a pier, it isn't going to travel far and is much more likely to be found.
I can think of only one case (a serial killer in Wyoming, I believe known as the lil' darling murder) where someone was abducted, killed and their body and vehicle concealed. In most cases where someone and their vehicle disappear, it turns out to be an accident. Some cases, of course, are never solved so we don't know.
If they did not have some mishap in the Delaware River near South St., they probably did not drive straight back to Mt. Laurel. The went somewhere else. It was a very cold night. They could have hit a patch of black ice alongside a body of water. I'm guessing they will be found some day.