For decades 88-year-old Wagner has refused to speak to police, and what exactly happened on that boat has remained a mystery.
But since the case was reopened in 2011, more than 100 new witnesses have come forward and 150 new clues have been uncovered, Closer reports today.
The US publication has uncovered a never-before-published 2014 interview with Wagner in which he explosively reveals what happened.
'I have many, many memories of her,' he said. 'She was such a special lady to me and everyone in the family.'
Closer reports that as investigators try to piece together the new evidence, and come nearer to solving the case, a very different picture of Wood and Wagner's marriage has emerged.
The LA coroner's office has changed the manner of Wood's death from 'accidental drowning' to 'drowning and other undetermined factors', Closer claims.
In his 2008 memoir, Pieces of My Heart, Wagner revealed: 'A minute can change anything.'
Robert claims, 'The last time I saw my wife, she was fixing her hair at a little vanity in the bathroom.'
Closer reveals Wagner's theory is that Wood 'slipped.'
'She heard the dinghy banging against the side and got up to retie it,' Closer reveals the star as saying, noting Wagner as recalling Wood had had 'seven or eight' glasses of wine. 'She slipped on the swim step on the stern, hit the step on the way down, and was either stunned or knocked unconscious and rolled into the water.'
The case of Wood's death remains open.