7:53 AM PT -- 9/28 -- According to our sources ... the possible evidence that Brian's parents were at the campsite are 2 camping reservations under their name from Sept. 1-3 and Sept. 6-8. It's been reported the Laundries were seen driving with a small camper, so it's believed this is where they went ... but there's only speculation Brian was with them.
We're told Dog received a tip that Brian was spotted at the campsite as recently as Saturday, and he plans to head to the Fort DeSoto Park area himself to continue tracking leads he's received.
Dog the Bounty Hunter is right on Brian Laundrie's tail ... or at least it's possible, and authorities are looking into it.
A source with direct knowledge tells TMZ ... Dog -- who joined the manhunt for Gabby Petito's fiance a couple days ago -- has been in the Florida woods looking for him, and found something he thinks may finally lead to his capture.