Yes, I do. They discovered the murderer's profile and reached out to law enforcement with the details, including his chilling statement of intent. They could have silently deleted the profile and deflected criticism from themselves.
I am not aware of anything resembling 'archival links' other than screenshots of only the most recent posts, and verbal reports from others as to past posts.
One single page of vileness. No 'likes' to his posts, so not very popular. Notable is the anti-Trump sentiment. Not enough to confirm that this profile actually belonged to Robert Brower since names and profile pictures can be misappropriated.
Meanwhile, Gab was able to provide a complete profile of this individual and confirmation of his identity to the authorities.