It is entirely possible to kill someone and despose of the body in a way it will never be found. Easiest method is to know the currents of the ocean and bury the body at sea.
Entirely possible for the mob to put the body on a large boat, weight it down, and dump it overboard in the blue ocean. Think of all the sailors buried at sea. They don't wash up on shore.
If you don't want to do all that, then feed the body to a group of gators!
Or, sew the body up on a bag with weights imbedded all over. Fly the body in an airplane over the middle of the ocean, and dump the body from a few thousand feet and let gravity do the job.
He's obviously dead, and after all these years, I don't think his body will ever be found. Just like Natalie Holloway.
Ken