The details of the vehicle are of the interior, which doesn't help much unless you've been in it. That doesn't help most people. If someone had a similar interior then you would guess LE could at least narrow down a make or model. The details which have been released aren't that helpful, even to those who may know him. While it is a good idea to keep info close to the vest, there may be something about the words he uses or an item that may help others recognize him. The longer they go without an arrest the chances diminish that they will find him. They've had the evidence for weeks now.
With no one coming forward about the thong I wonder if he didn't buy it and later add DNA to it. I know that's a stretch but it would explain no one claiming it. If the arsehole is so into undies then it wouldn't be that difficult to transfer DNA from another pair he has that could be traced. Or maybe he has had it for years. If it was just regular underwear then I could see the difficulty in finding it's owner. Most women wouldn't know if a pair of UW was missing because they often buy them in packs of 3 or more. I know I don't keep close tabs on my undies. However, the thong is distinctive.