Me too. I love Walken. I hope he will come forward and crack the case somehow!
My theory has been that Walken was in an impossible situation. He wasn't a big name actor at the time and had zero clout in the industry. He may have been threatened by "fixers" who helped cover up the facts to protect Wagner. (They probably also rationalized the coverup was to help Natalie's good reputation and legacy). Walken probably gave his account to police, but since they were involved in the cover up, it's probably still in a filing cabinet somewhere.
My theory of the scenario: Everyone had a lot to drink. Natalie went to bed. Later the others went to bed, too. Natalie and RW got into an argument, she was angry and wanted to get off the boat to get away from RZ. He may have even gotten pushy with her. She put on her down jacket (that she was wearing when found) and went out to demand someone take her to shore, probably in the inflatable boat. RW followed, more arguing. Trying to climb over the boat a scuffle ensued between RW and NW. She fell into the water instead of the boat. Somewhere in the scuffle she got all those bruises on the backs of her legs.
NW starts calling for help, the other two men come out to try to help her, but RW says to leave her alone, she's just being dramatic or something. He probably threatened their jobs, careers, etc. They argue with him, but eventually realize NW has stopped screaming. With the heavy, wet down coat, she probably drowned quickly. They scramble to get her and see she's dead. RW freaks out, calls a "fixer" (usually a powerful attorney in the movie biz) who pulls some strings and gets a plan in place.
The excuse used is, it's a terrible accident, nothing can bring her back, etc. LE, ME, etc. are all paid off to make it look as much like an accident as possible. The story is changed slightly to say everyone else was asleep when she got into the dinghy and fell. I still wonder if some of the bruising on the back of her legs happened when she was pulled back into the boat while trying to get off or if she fell on board the boat and RW dragged her around.
JMO, Walken tried to do what he could to help, but was threatened by RW and the drowning actually happened pretty quickly, before they could convince RW to let them help her. I've always had the perception from him that he was very upset with what happened, but felt he did all he could to help. He may regret not getting physical with RW, but it may not have made any difference. It would have taken two or more people to get her out of the water and back into the boat. It was a big boat that sat high off the water and someone on board would have had to help get them up, esp in the dark.
I really liked him in "The Deer Hunter" and hoped to see him in a lot more movies. He didn't get a lot of good parts for years afterwards (no movie roles from '83 to ,85), probably as a way to pressure him into keeping quiet.
All JMO :twocents:
ETA: I'm also guessing those involved in applying pressure to cover up the real story are very high on the political ladder, possibly even going all the way to the WH at the time. For that reason, some still want to keep this covered up. Not to protect RW, but to avoid tarnishing the reputation of some powerful folks in the cover up. JMO