Do you think there was any crash material hidden away by witnesses of the 1947 Roswell UFO crash?
But of course...
Before answering the question, let's get the terminology right.
What crashed at Roswell was a balloon designed to monitor nuclear tests. No mystery. The US Air Force admitted this in the 1990s and released the official documents from 1947 to prove it.
Now to answer your question, which we can edit in light of the above to be "did anybody hide away bits of the balloon?"
Maybe. There are photos from the time of people holding what are obviously bits of balloon material.
However, Cold War paranoia led some people to scream "Aliens!!!" out of ignorance of what a crashed balloon looks like.
Some other people saw an opportunity to fleece the gullible and started screaming "Aliens!!" too, in order to sell their books.
The gullible lapped all this nonsense up, and still do. Roswell is a profitable industry.
The fact that official proof of the complete lack of mystery about Roswell has not dented the money-making ability of the yarn tells you we're in the depressingly-familiar and intelligence-free territory of American paranoia (cf. Chemtrails, flat earthers, antivaxxers, etc. etc. etc.).
See here: Roswell UFO incident - Wikipedia
I don't think there is. It seems to me that they would have come forward with the materials by now. I'm surprised there hasn't been a major private effort to go back there and really go over that site very extensively to look for pieces of that UFO.