I may be wrong, but I think he was the last surviving witness.
The info on the case can be found here.
In his report on the incident for Lockheed, Wimmer, a top test pilot, wrote:
I was watching it all the time so I was able to see it for several seconds after the rest of the crew had lost sight of it. Right up until the time it disappeared it maintained its sharp outline and definite shape so I know it was not a cloud that dissolved... I am convinced this was a large object some distance away.Of course, the United States Air Force, in one of their most bone-headed explanations ever (and that's saying something), concluded that what Wimmer and other top Lockheed personnel (including Kelly Johnson) saw that day was a lenticular cloud.
My condolences to Mr. Wimmer's family.