It's a lie! The evidence was totally fabricated! In fact, during the Warren Commission hearings, a photo of Walker's house that was allegedly found at the Oswalds' apartment was first shown to Marina Oswald and she knew nothing about it. When admitted into evidence later, the photograph had been altered by removing the license plate! A photo of Police Chief Curry accidentally included the doctored photograph. The photo was taken before the Warren Comission hearings and clearly shows the license plate is visible!
Oh..sorry. Slipped into CT mode for a moment. The part about the photo above is nearly true. It is the conspiracists' version of events. The photo in question was damaged, and the license plate was removed, presumably by Oswald himself. The photo of Chief Curry did include the photograph, but the reason it appears undamaged was a difficult to view camera angle. (And I might have gotten a few details wrong. It has been 20 years since I looked into it.)
So, yeah, I knew about it. However, I'm a bit more knowledgeable than most about the JFK conspiracy theories. They had a lot to do with my journey to skepticism in general. My dad was a very smart guy, and a conspiracy theorist. Growing up, I tended to believe what he said, and I read a couple of conspiracy books and believed them. (I remember "Six Seconds in Dallas".) One day in my college library I stumbled on the Warren Report and picked it up, looking to see what those rotten conspirators had tried to pass off on the American people and discovered, to my surprise, that it was quite reasonable, and that the conspiracy books hadn't even gotten its contents correct. It sort of led me to become a bit of an assassination buff, but on the anti-conspiracy side.
It also taught me that there is a difference between being smart and being right. After that, I tended to take my dad's beliefs with a bit larger grain of salt. I eventually came to see him as a loveable, intelligent, but somewhat kooky, fellow.
FWIW, Marina also knew about the Walker attempt. It was a big reason why she was very frightened after the assassination of JFK. She was afraid that she would be arrested or deported for knowing about the crime, and not going to the polce.