What do you mean you can’t share the file using VLC? VLC is for playing videos. You aren’t supposed to share through playback software.
All you need to do to if you want to give the file to the police is give them the flash drive. If you want to keep a local copy, then simply copy it over to your computer before giving it to them. Or if they want it on their flash drive, you copy it to your computer, then copy it to their flash drive.
Alternately, I know some people who upload the videos to their Google Drive and share from there.