Rebecca, from Guilden Sutton, disappeared in March 2011 while working on a cruise ship sailing between Los Angeles and Mexico.
Chester MP Chris Matheson, who is coordinating the campaign to uncover the truth behind Rebecca’s disappearance, welcomed Mr Ramm’s involvement.
“We are really grateful that Commander Ramm has offered to assist us with this investigation. He was one of the most senior police officers in the country and is a hugely experienced detective. His expertise and knowledge will be invaluable.
“Bringing Roy into the team feels like we are now moving the big guns on to the field of play.”
Chris concluded: “People need to understand that this story just isn’t going to go away. We already have a large bunch of evidence and our team will keep working to get more. To those reading this, perhaps online abroad, who have information about this case, I suggest you get in contact with us, because we’re not stopping now.”