Well, lets see . . . we can guess that whoever went in, went in to murder them, because he didn't rob anything.
He had on a motorcycle helmet, probably so he wouldn't be recognized or described by neighbors, but he must have not cared if the Husteds recognized him. Also, he must have put it on just before he came in, because he came in the door facing the beach, and everybody around would notice someone on the beach wearing a motorcycle helmet.
He was wearing a jumpsuit or coveralls, to maybe protect his clothes from the blood? He could have peeled that off and walked down the beach or into some nearby landscaping and over to his car (if he drove one there.)
The neighbors say they didn't hear a motorcycle in the area.
To tell you the truth, I would be looking at whether there may be a murderer in the neighborhood. Maybe someone developed a fixation on Mrs. Husted or someone wanted to try out murdering people. Let's hope they find those coveralls (or the knife or helmet) soon.