See, the dogs thing makes my head spin. I have to look back but I thought one dogspert said that they could have picked up the scent left from the previous day, and another said they may have picked it up from the belongings?
I just don't know enough about dogs and their complexity to speak to that, but IIRC, there wasn't a definitive answer as to what the dogs' hit actually signified.
But like I said- that subject confuses me!!!
Okay, I'm a verified dog trainer on WS and I have some experience with SAR dogs. I started watching scent work as a teenager when I fox hunted (a sport that is usually blood free and way too fun).
Your ordinary every day house pet with no training at all will tend to track from the oldest scent to the newest scent. It's instinct. Mother Nature didn't let proto-wolves that tracked backwards eat often enough to reproduce. Fifi the Chihuahua will naturally do this between her stints on the couch eating bonbons.
Humans, we are not so bright about scent and tracking. I suspect that dogs are certain we are noseblind and hence mentally impaired. An
inexperienced human can manage to train their dog to track backwards. It's a common mistake for newbie tracking handlers to make.
However, the FBI doesn't spend money to fly in newbie handlers to incident scenes. FBI handlers are experienced and have the training logs detailing thousands of hours of training and the results so that they can testify in court if need be.
So I think we can rule out two FBI handler/dog teams making the exact same newbie handler mistake of teaching a dog to track from newest to oldest scent. Sure, dogs make mistakes but the exact same mistake? Nah.
If the newest scent was on the bicycles, the dogs should have cast around and just kept going back to the bicycles, saying with their behaviour "newest scent is right here on these bikes, boss."
As for picking up scent left by belongings in other places. There is lots and lots of research (mostly carried out by the DoD) that supports the idea that dogs are tracking the millions of skin cells that fall off the human body every day. They are called skin
rafts because they aren't just skin cells, they also have skin lipids (oil) plus the bacteria and fungus that colonise every normal human being's skin.
It is possible to lay a scent using something that belongs to someone. Ideal would be to use a piece of clothing that had been worn for hours, got good and sweaty. Dragging that item along the ground will leave a trail that a dog will follow. The part of the item that has been in contact with the human being should be dragged on the ground to leave a scent. Carrying the item along off the ground without touching anything will not lay enough of a track for most dogs to work in a committed manner.
Again, the dog will follow a drag from the oldest to the newest scent.
We
know where the bikes ended up. If they had been used as drags, the newest scent would, again, be right there on the bicycles.
According to uneducated observers and supported by Sandy Breault's comments about the dogs indicating that the girls' scent was found lakeside by the dogs, I think we can rule out the bikes having been used as drags.
So, I've gotta go with Sandy Breault: the dogs indicated that the girls were at the lake that day.
...can I talk about fox hunting now? <just kidding>
Sorry. 
